[V2,RFC,2/3] svcrdma: Recvfrom changes

Message ID	20140506174632.18208.28160.stgit@build.ogc.int (mailing list archive)
State	Rejected
Headers	show Return-Path: <linux-rdma-owner@kernel.org> From: Steve Wise <swise@opengridcomputing.com> Subject: [PATCH V2 RFC 2/3] svcrdma: Recvfrom changes To: bfields@fieldses.org Cc: linux-nfs@vger.kernel.org, linux-rdma@vger.kernel.org, tom@opengridcomputing.com Date: Tue, 06 May 2014 12:46:32 -0500 Message-ID: <20140506174632.18208.28160.stgit@build.ogc.int> In-Reply-To: <20140506174621.18208.24242.stgit@build.ogc.int> References: <20140506174621.18208.24242.stgit@build.ogc.int> User-Agent: StGIT/0.14.3 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-rdma-owner@vger.kernel.org Precedence: bulk

Steve Wise May 6, 2014, 5:46 p.m. UTC

From: Tom Tucker <tom@opengridcomputing.com>

Based on device support, RDMA read target sgls are fast-registered,
or composed using the local dma lkey or a dma_mr lkey.  A given NFS
Write chunk list will be split into a set of rdma reads based on the
limitations of the device.

Signed-off-by: Tom Tucker <tom@opengridcomputing.com>
Signed-off-by: Steve Wise <swise@opengridcomputing.com>
---

 net/sunrpc/xprtrdma/svc_rdma_recvfrom.c |  633 +++++++++++++------------------
 1 files changed, 259 insertions(+), 374 deletions(-)


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Chuck Lever May 13, 2014, 6:22 p.m. UTC | #1

Hi Steve-

Some random review comments, see below.


On May 6, 2014, at 1:46 PM, Steve Wise <swise@opengridcomputing.com> wrote:

> From: Tom Tucker <tom@opengridcomputing.com>
> 
> Based on device support, RDMA read target sgls are fast-registered,
> or composed using the local dma lkey or a dma_mr lkey.  A given NFS
> Write chunk list will be split into a set of rdma reads based on the
> limitations of the device.
> 
> Signed-off-by: Tom Tucker <tom@opengridcomputing.com>
> Signed-off-by: Steve Wise <swise@opengridcomputing.com>
> ---
> 
> net/sunrpc/xprtrdma/svc_rdma_recvfrom.c |  633 +++++++++++++------------------
> 1 files changed, 259 insertions(+), 374 deletions(-)
> 
> diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> index 8d904e4..1c4c285 100644
> --- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> +++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
> @@ -1,4 +1,5 @@
> /*
> + * Copyright (c) 2014 Open Grid Computing, Inc. All rights reserved.
>  * Copyright (c) 2005-2006 Network Appliance, Inc. All rights reserved.
>  *
>  * This software is available to you under a choice of one of two
> @@ -69,7 +70,8 @@ static void rdma_build_arg_xdr(struct svc_rqst *rqstp,
> 
> 	/* Set up the XDR head */
> 	rqstp->rq_arg.head[0].iov_base = page_address(page);
> -	rqstp->rq_arg.head[0].iov_len = min(byte_count, ctxt->sge[0].length);
> +	rqstp->rq_arg.head[0].iov_len =
> +		min_t(size_t, byte_count, ctxt->sge[0].length);
> 	rqstp->rq_arg.len = byte_count;
> 	rqstp->rq_arg.buflen = byte_count;
> 
> @@ -85,7 +87,7 @@ static void rdma_build_arg_xdr(struct svc_rqst *rqstp,
> 		page = ctxt->pages[sge_no];
> 		put_page(rqstp->rq_pages[sge_no]);
> 		rqstp->rq_pages[sge_no] = page;
> -		bc -= min(bc, ctxt->sge[sge_no].length);
> +		bc -= min_t(u32, bc, ctxt->sge[sge_no].length);
> 		rqstp->rq_arg.buflen += ctxt->sge[sge_no].length;
> 		sge_no++;
> 	}
> @@ -113,291 +115,249 @@ static void rdma_build_arg_xdr(struct svc_rqst *rqstp,
> 	rqstp->rq_arg.tail[0].iov_len = 0;
> }
> 
> -/* Encode a read-chunk-list as an array of IB SGE
> - *
> - * Assumptions:
> - * - chunk[0]->position points to pages[0] at an offset of 0
> - * - pages[] is not physically or virtually contiguous and consists of
> - *   PAGE_SIZE elements.
> - *
> - * Output:
> - * - sge array pointing into pages[] array.
> - * - chunk_sge array specifying sge index and count for each
> - *   chunk in the read list
> - *
> - */
> -static int map_read_chunks(struct svcxprt_rdma *xprt,
> -			   struct svc_rqst *rqstp,
> -			   struct svc_rdma_op_ctxt *head,
> -			   struct rpcrdma_msg *rmsgp,
> -			   struct svc_rdma_req_map *rpl_map,
> -			   struct svc_rdma_req_map *chl_map,
> -			   int ch_count,
> -			   int byte_count)
> +static int rdma_read_max_sge(struct svcxprt_rdma *xprt, int sge_count)
> {
> -	int sge_no;
> -	int sge_bytes;
> -	int page_off;
> -	int page_no;
> -	int ch_bytes;
> -	int ch_no;
> -	struct rpcrdma_read_chunk *ch;
> +	if (rdma_node_get_transport(xprt->sc_cm_id->device->node_type) ==
> +	     RDMA_TRANSPORT_IWARP)
> +		return 1;
> +	else
> +		return min_t(int, sge_count, xprt->sc_max_sge);
> +}
> 
> -	sge_no = 0;
> -	page_no = 0;
> -	page_off = 0;
> -	ch = (struct rpcrdma_read_chunk *)&rmsgp->rm_body.rm_chunks[0];
> -	ch_no = 0;
> -	ch_bytes = ntohl(ch->rc_target.rs_length);
> -	head->arg.head[0] = rqstp->rq_arg.head[0];
> -	head->arg.tail[0] = rqstp->rq_arg.tail[0];
> -	head->arg.pages = &head->pages[head->count];
> -	head->hdr_count = head->count; /* save count of hdr pages */
> -	head->arg.page_base = 0;
> -	head->arg.page_len = ch_bytes;
> -	head->arg.len = rqstp->rq_arg.len + ch_bytes;
> -	head->arg.buflen = rqstp->rq_arg.buflen + ch_bytes;
> -	head->count++;
> -	chl_map->ch[0].start = 0;
> -	while (byte_count) {
> -		rpl_map->sge[sge_no].iov_base =
> -			page_address(rqstp->rq_arg.pages[page_no]) + page_off;
> -		sge_bytes = min_t(int, PAGE_SIZE-page_off, ch_bytes);
> -		rpl_map->sge[sge_no].iov_len = sge_bytes;
> -		/*
> -		 * Don't bump head->count here because the same page
> -		 * may be used by multiple SGE.
> -		 */
> -		head->arg.pages[page_no] = rqstp->rq_arg.pages[page_no];
> -		rqstp->rq_respages = &rqstp->rq_arg.pages[page_no+1];
> +typedef int (*rdma_reader_fn)(struct svcxprt_rdma *xprt,
> +			      struct svc_rqst *rqstp,
> +			      struct svc_rdma_op_ctxt *head,
> +			      int *page_no,
> +			      u32 *page_offset,
> +			      u32 rs_handle,
> +			      u32 rs_length,
> +			      u64 rs_offset,
> +			      int last);
> +
> +/* Issue an RDMA_READ using the local lkey to map the data sink */
> +static int rdma_read_chunk_lcl(struct svcxprt_rdma *xprt,
> +			       struct svc_rqst *rqstp,
> +			       struct svc_rdma_op_ctxt *head,
> +			       int *page_no,
> +			       u32 *page_offset,
> +			       u32 rs_handle,
> +			       u32 rs_length,
> +			       u64 rs_offset,
> +			       int last)
> +{
> +	struct ib_send_wr read_wr;
> +	int pages_needed = PAGE_ALIGN(*page_offset + rs_length) >> PAGE_SHIFT;
> +	struct svc_rdma_op_ctxt *ctxt = svc_rdma_get_context(xprt);
> +	int ret, read, pno;
> +	u32 pg_off = *page_offset;
> +	u32 pg_no = *page_no;
> +
> +	ctxt->direction = DMA_FROM_DEVICE;
> +	ctxt->read_hdr = head;
> +	pages_needed =
> +		min_t(int, pages_needed, rdma_read_max_sge(xprt, pages_needed));
> +	read = min_t(int, pages_needed << PAGE_SHIFT, rs_length);
> +
> +	for (pno = 0; pno < pages_needed; pno++) {
> +		int len = min_t(int, rs_length, PAGE_SIZE - pg_off);
> +
> +		head->arg.pages[pg_no] = rqstp->rq_arg.pages[pg_no];
> +		head->arg.page_len += len;
> +		head->arg.len += len;
> +		head->count++;
> +		rqstp->rq_respages = &rqstp->rq_arg.pages[pg_no+1];
> 		rqstp->rq_next_page = rqstp->rq_respages + 1;
> +		ctxt->sge[pno].addr =
> +			ib_dma_map_page(xprt->sc_cm_id->device,
> +					head->arg.pages[pg_no], pg_off,
> +					PAGE_SIZE - pg_off,
> +					DMA_FROM_DEVICE);
> +		ret = ib_dma_mapping_error(xprt->sc_cm_id->device,
> +					   ctxt->sge[pno].addr);
> +		if (ret)
> +			goto err;
> +		atomic_inc(&xprt->sc_dma_used);
> 
> -		byte_count -= sge_bytes;
> -		ch_bytes -= sge_bytes;
> -		sge_no++;
> -		/*
> -		 * If all bytes for this chunk have been mapped to an
> -		 * SGE, move to the next SGE
> -		 */
> -		if (ch_bytes == 0) {
> -			chl_map->ch[ch_no].count =
> -				sge_no - chl_map->ch[ch_no].start;
> -			ch_no++;
> -			ch++;
> -			chl_map->ch[ch_no].start = sge_no;
> -			ch_bytes = ntohl(ch->rc_target.rs_length);
> -			/* If bytes remaining account for next chunk */
> -			if (byte_count) {
> -				head->arg.page_len += ch_bytes;
> -				head->arg.len += ch_bytes;
> -				head->arg.buflen += ch_bytes;
> -			}
> -		}
> -		/*
> -		 * If this SGE consumed all of the page, move to the
> -		 * next page
> -		 */
> -		if ((sge_bytes + page_off) == PAGE_SIZE) {
> -			page_no++;
> -			page_off = 0;
> -			/*
> -			 * If there are still bytes left to map, bump
> -			 * the page count
> -			 */
> -			if (byte_count)
> -				head->count++;
> -		} else
> -			page_off += sge_bytes;
> +		/* The lkey here is either a local dma lkey or a dma_mr lkey */
> +		ctxt->sge[pno].lkey = xprt->sc_dma_lkey;
> +		ctxt->sge[pno].length = len;
> +		ctxt->count++;
> +
> +		pg_no++;
> +		pg_off = 0;
> +		rs_length -= len;
> +	}
> +
> +	if (last && rs_length == 0)
> +		set_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags);
> +	else
> +		clear_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags);
> +
> +	memset(&read_wr, 0, sizeof(read_wr));
> +	read_wr.wr_id = (unsigned long)ctxt;
> +	read_wr.opcode = IB_WR_RDMA_READ;
> +	ctxt->wr_op = read_wr.opcode;
> +	read_wr.send_flags = IB_SEND_SIGNALED;
> +	read_wr.wr.rdma.rkey = rs_handle;
> +	read_wr.wr.rdma.remote_addr = rs_offset;
> +	read_wr.sg_list = ctxt->sge;
> +	read_wr.num_sge = pages_needed;
> +
> +	ret = svc_rdma_send(xprt, &read_wr);
> +	if (ret) {
> +		pr_err("svcrdma: Error %d posting RDMA_READ\n", ret);
> +		set_bit(XPT_CLOSE, &xprt->sc_xprt.xpt_flags);
> +		goto err;
> 	}
> -	BUG_ON(byte_count != 0);
> -	return sge_no;
> +	*page_no = pg_no;
> +	*page_offset = pg_off;
> +	ret = read;
> +	atomic_inc(&rdma_stat_read);
> +	return ret;
> + err:
> +	svc_rdma_unmap_dma(ctxt);
> +	svc_rdma_put_context(ctxt, 0);
> +	return ret;
> }
> 
> -/* Map a read-chunk-list to an XDR and fast register the page-list.
> - *
> - * Assumptions:
> - * - chunk[0]	position points to pages[0] at an offset of 0
> - * - pages[]	will be made physically contiguous by creating a one-off memory
> - *		region using the fastreg verb.
> - * - byte_count is # of bytes in read-chunk-list
> - * - ch_count	is # of chunks in read-chunk-list
> - *
> - * Output:
> - * - sge array pointing into pages[] array.
> - * - chunk_sge array specifying sge index and count for each
> - *   chunk in the read list
> - */
> -static int fast_reg_read_chunks(struct svcxprt_rdma *xprt,
> +/* Issue an RDMA_READ using an FRMR to map the data sink */
> +static int rdma_read_chunk_frmr(struct svcxprt_rdma *xprt,
> 				struct svc_rqst *rqstp,
> 				struct svc_rdma_op_ctxt *head,
> -				struct rpcrdma_msg *rmsgp,
> -				struct svc_rdma_req_map *rpl_map,
> -				struct svc_rdma_req_map *chl_map,
> -				int ch_count,
> -				int byte_count)
> +				int *page_no,
> +				u32 *page_offset,
> +				u32 rs_handle,
> +				u32 rs_length,
> +				u64 rs_offset,
> +				int last)
> {
> -	int page_no;
> -	int ch_no;
> -	u32 offset;
> -	struct rpcrdma_read_chunk *ch;
> -	struct svc_rdma_fastreg_mr *frmr;
> -	int ret = 0;
> +	struct ib_send_wr read_wr;
> +	struct ib_send_wr inv_wr;
> +	struct ib_send_wr fastreg_wr;
> +	u8 key;
> +	int pages_needed = PAGE_ALIGN(*page_offset + rs_length) >> PAGE_SHIFT;
> +	struct svc_rdma_op_ctxt *ctxt = svc_rdma_get_context(xprt);
> +	struct svc_rdma_fastreg_mr *frmr = svc_rdma_get_frmr(xprt);
> +	int ret, read, pno;
> +	u32 pg_off = *page_offset;
> +	u32 pg_no = *page_no;
> 
> -	frmr = svc_rdma_get_frmr(xprt);
> 	if (IS_ERR(frmr))
> 		return -ENOMEM;
> 
> -	head->frmr = frmr;
> -	head->arg.head[0] = rqstp->rq_arg.head[0];
> -	head->arg.tail[0] = rqstp->rq_arg.tail[0];
> -	head->arg.pages = &head->pages[head->count];
> -	head->hdr_count = head->count; /* save count of hdr pages */
> -	head->arg.page_base = 0;
> -	head->arg.page_len = byte_count;
> -	head->arg.len = rqstp->rq_arg.len + byte_count;
> -	head->arg.buflen = rqstp->rq_arg.buflen + byte_count;
> +	ctxt->direction = DMA_FROM_DEVICE;
> +	ctxt->frmr = frmr;
> +	pages_needed = min_t(int, pages_needed, xprt->sc_frmr_pg_list_len);
> +	read = min_t(int, pages_needed << PAGE_SHIFT, rs_length);
> 
> -	/* Fast register the page list */
> -	frmr->kva = page_address(rqstp->rq_arg.pages[0]);
> +	frmr->kva = page_address(rqstp->rq_arg.pages[pg_no]);
> 	frmr->direction = DMA_FROM_DEVICE;
> 	frmr->access_flags = (IB_ACCESS_LOCAL_WRITE|IB_ACCESS_REMOTE_WRITE);
> -	frmr->map_len = byte_count;
> -	frmr->page_list_len = PAGE_ALIGN(byte_count) >> PAGE_SHIFT;
> -	for (page_no = 0; page_no < frmr->page_list_len; page_no++) {
> -		frmr->page_list->page_list[page_no] =
> +	frmr->map_len = pages_needed << PAGE_SHIFT;
> +	frmr->page_list_len = pages_needed;
> +
> +	for (pno = 0; pno < pages_needed; pno++) {
> +		int len = min_t(int, rs_length, PAGE_SIZE - pg_off);
> +
> +		head->arg.pages[pg_no] = rqstp->rq_arg.pages[pg_no];
> +		head->arg.page_len += len;
> +		head->arg.len += len;
> +		head->count++;
> +		rqstp->rq_respages = &rqstp->rq_arg.pages[pg_no+1];
> +		rqstp->rq_next_page = rqstp->rq_respages + 1;
> +		frmr->page_list->page_list[pno] =
> 			ib_dma_map_page(xprt->sc_cm_id->device,
> -					rqstp->rq_arg.pages[page_no], 0,
> +					head->arg.pages[pg_no], 0,
> 					PAGE_SIZE, DMA_FROM_DEVICE);
> -		if (ib_dma_mapping_error(xprt->sc_cm_id->device,
> -					 frmr->page_list->page_list[page_no]))
> -			goto fatal_err;
> +		ret = ib_dma_mapping_error(xprt->sc_cm_id->device,
> +					   frmr->page_list->page_list[pno]);
> +		if (ret)
> +			goto err;
> 		atomic_inc(&xprt->sc_dma_used);
> -		head->arg.pages[page_no] = rqstp->rq_arg.pages[page_no];
> +		pg_no++;
> +		pg_off = 0;
> 	}
> -	head->count += page_no;
> 
> -	/* rq_respages points one past arg pages */
> -	rqstp->rq_respages = &rqstp->rq_arg.pages[page_no];
> -	rqstp->rq_next_page = rqstp->rq_respages + 1;
> +	if (last && read == rs_length)
> +		set_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags);
> +	else
> +		clear_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags);
> 
> -	/* Create the reply and chunk maps */
> -	offset = 0;
> -	ch = (struct rpcrdma_read_chunk *)&rmsgp->rm_body.rm_chunks[0];
> -	for (ch_no = 0; ch_no < ch_count; ch_no++) {
> -		int len = ntohl(ch->rc_target.rs_length);
> -		rpl_map->sge[ch_no].iov_base = frmr->kva + offset;
> -		rpl_map->sge[ch_no].iov_len = len;
> -		chl_map->ch[ch_no].count = 1;
> -		chl_map->ch[ch_no].start = ch_no;
> -		offset += len;
> -		ch++;
> +	/* Bump the key */
> +	key = (u8)(frmr->mr->lkey & 0x000000FF);
> +	ib_update_fast_reg_key(frmr->mr, ++key);
> +
> +	ctxt->sge[0].addr = (unsigned long)frmr->kva;
> +	ctxt->sge[0].lkey = frmr->mr->lkey;
> +	ctxt->sge[0].length = read;
> +	ctxt->count = 1;
> +	ctxt->read_hdr = head;
> +
> +	/* Prepare FASTREG WR */
> +	memset(&fastreg_wr, 0, sizeof(fastreg_wr));
> +	fastreg_wr.opcode = IB_WR_FAST_REG_MR;
> +	fastreg_wr.send_flags = IB_SEND_SIGNALED;
> +	fastreg_wr.wr.fast_reg.iova_start = (unsigned long)frmr->kva;
> +	fastreg_wr.wr.fast_reg.page_list = frmr->page_list;
> +	fastreg_wr.wr.fast_reg.page_list_len = frmr->page_list_len;
> +	fastreg_wr.wr.fast_reg.page_shift = PAGE_SHIFT;
> +	fastreg_wr.wr.fast_reg.length = frmr->map_len;
> +	fastreg_wr.wr.fast_reg.access_flags = frmr->access_flags;
> +	fastreg_wr.wr.fast_reg.rkey = frmr->mr->lkey;
> +	fastreg_wr.next = &read_wr;
> +
> +	/* Prepare RDMA_READ */
> +	memset(&read_wr, 0, sizeof(read_wr));
> +	read_wr.send_flags = IB_SEND_SIGNALED;
> +	read_wr.wr.rdma.rkey = rs_handle;
> +	read_wr.wr.rdma.remote_addr = rs_offset;
> +	read_wr.sg_list = ctxt->sge;
> +	read_wr.num_sge = 1;
> +	if (xprt->sc_dev_caps & SVCRDMA_DEVCAP_READ_W_INV) {
> +		read_wr.opcode = IB_WR_RDMA_READ_WITH_INV;
> +		read_wr.wr_id = (unsigned long)ctxt;
> +		read_wr.ex.invalidate_rkey = ctxt->frmr->mr->lkey;
> +	} else {
> +		read_wr.opcode = IB_WR_RDMA_READ;
> +		read_wr.next = &inv_wr;
> +		/* Prepare invalidate */
> +		memset(&inv_wr, 0, sizeof(inv_wr));
> +		inv_wr.wr_id = (unsigned long)ctxt;
> +		inv_wr.opcode = IB_WR_LOCAL_INV;
> +		inv_wr.send_flags = IB_SEND_SIGNALED;
> +		inv_wr.ex.invalidate_rkey = frmr->mr->lkey;
> 	}
> -
> -	ret = svc_rdma_fastreg(xprt, frmr);
> -	if (ret)
> -		goto fatal_err;
> -
> -	return ch_no;
> -
> - fatal_err:
> -	printk("svcrdma: error fast registering xdr for xprt %p", xprt);
> -	svc_rdma_put_frmr(xprt, frmr);
> -	return -EIO;
> -}
> -
> -static int rdma_set_ctxt_sge(struct svcxprt_rdma *xprt,
> -			     struct svc_rdma_op_ctxt *ctxt,
> -			     struct svc_rdma_fastreg_mr *frmr,
> -			     struct kvec *vec,
> -			     u64 *sgl_offset,
> -			     int count)
> -{
> -	int i;
> -	unsigned long off;
> -
> -	ctxt->count = count;
> -	ctxt->direction = DMA_FROM_DEVICE;
> -	for (i = 0; i < count; i++) {
> -		ctxt->sge[i].length = 0; /* in case map fails */
> -		if (!frmr) {
> -			BUG_ON(!virt_to_page(vec[i].iov_base));
> -			off = (unsigned long)vec[i].iov_base & ~PAGE_MASK;
> -			ctxt->sge[i].addr =
> -				ib_dma_map_page(xprt->sc_cm_id->device,
> -						virt_to_page(vec[i].iov_base),
> -						off,
> -						vec[i].iov_len,
> -						DMA_FROM_DEVICE);
> -			if (ib_dma_mapping_error(xprt->sc_cm_id->device,
> -						 ctxt->sge[i].addr))
> -				return -EINVAL;
> -			ctxt->sge[i].lkey = xprt->sc_dma_lkey;
> -			atomic_inc(&xprt->sc_dma_used);
> -		} else {
> -			ctxt->sge[i].addr = (unsigned long)vec[i].iov_base;
> -			ctxt->sge[i].lkey = frmr->mr->lkey;
> -		}
> -		ctxt->sge[i].length = vec[i].iov_len;
> -		*sgl_offset = *sgl_offset + vec[i].iov_len;
> +	ctxt->wr_op = read_wr.opcode;
> +
> +	/* Post the chain */
> +	ret = svc_rdma_send(xprt, &fastreg_wr);
> +	if (ret) {
> +		pr_err("svcrdma: Error %d posting RDMA_READ\n", ret);
> +		set_bit(XPT_CLOSE, &xprt->sc_xprt.xpt_flags);
> +		goto err;
> 	}
> -	return 0;
> -}
> -
> -static int rdma_read_max_sge(struct svcxprt_rdma *xprt, int sge_count)
> -{
> -	if ((rdma_node_get_transport(xprt->sc_cm_id->device->node_type) ==
> -	     RDMA_TRANSPORT_IWARP) &&
> -	    sge_count > 1)
> -		return 1;
> -	else
> -		return min_t(int, sge_count, xprt->sc_max_sge);
> +	*page_no = pg_no;
> +	*page_offset = pg_off;
> +	ret = read;
> +	atomic_inc(&rdma_stat_read);
> +	return ret;
> + err:
> +	svc_rdma_unmap_dma(ctxt);
> +	svc_rdma_put_context(ctxt, 0);
> +	svc_rdma_put_frmr(xprt, frmr);
> +	return ret;
> }
> 
> -/*
> - * Use RDMA_READ to read data from the advertised client buffer into the
> - * XDR stream starting at rq_arg.head[0].iov_base.
> - * Each chunk in the array
> - * contains the following fields:
> - * discrim      - '1', This isn't used for data placement
> - * position     - The xdr stream offset (the same for every chunk)
> - * handle       - RMR for client memory region
> - * length       - data transfer length
> - * offset       - 64 bit tagged offset in remote memory region
> - *
> - * On our side, we need to read into a pagelist. The first page immediately
> - * follows the RPC header.
> - *
> - * This function returns:
> - * 0 - No error and no read-list found.
> - *
> - * 1 - Successful read-list processing. The data is not yet in
> - * the pagelist and therefore the RPC request must be deferred. The
> - * I/O completion will enqueue the transport again and
> - * svc_rdma_recvfrom will complete the request.
> - *
> - * <0 - Error processing/posting read-list.
> - *
> - * NOTE: The ctxt must not be touched after the last WR has been posted
> - * because the I/O completion processing may occur on another
> - * processor and free / modify the context. Ne touche pas!
> - */
> -static int rdma_read_xdr(struct svcxprt_rdma *xprt,
> -			 struct rpcrdma_msg *rmsgp,
> -			 struct svc_rqst *rqstp,
> -			 struct svc_rdma_op_ctxt *hdr_ctxt)
> +static int rdma_read_chunks(struct svcxprt_rdma *xprt,
> +			    struct rpcrdma_msg *rmsgp,
> +			    struct svc_rqst *rqstp,
> +			    struct svc_rdma_op_ctxt *head)
> {
> -	struct ib_send_wr read_wr;
> -	struct ib_send_wr inv_wr;
> -	int err = 0;
> -	int ch_no;
> -	int ch_count;
> -	int byte_count;
> -	int sge_count;
> -	u64 sgl_offset;
> +	int page_no, ch_count, ret;
> 	struct rpcrdma_read_chunk *ch;
> -	struct svc_rdma_op_ctxt *ctxt = NULL;
> -	struct svc_rdma_req_map *rpl_map;
> -	struct svc_rdma_req_map *chl_map;
> +	u32 page_offset, byte_count;
> +	u64 rs_offset;
> +	rdma_reader_fn reader;
> 
> 	/* If no read list is present, return 0 */
> 	ch = svc_rdma_get_read_chunk(rmsgp);
> @@ -408,122 +368,53 @@ static int rdma_read_xdr(struct svcxprt_rdma *xprt,
> 	if (ch_count > RPCSVC_MAXPAGES)
> 		return -EINVAL;

I’m not sure what this ^^^ ch_count check is doing, but maybe I haven’t had
enough caffeine this morning. Shouldn’t this code be comparing the segment
count, not the chunk count, with MAXPAGES?


> 
> -	/* Allocate temporary reply and chunk maps */
> -	rpl_map = svc_rdma_get_req_map();
> -	chl_map = svc_rdma_get_req_map();
> -
> -	if (!xprt->sc_frmr_pg_list_len)
> -		sge_count = map_read_chunks(xprt, rqstp, hdr_ctxt, rmsgp,
> -					    rpl_map, chl_map, ch_count,
> -					    byte_count);
> -	else
> -		sge_count = fast_reg_read_chunks(xprt, rqstp, hdr_ctxt, rmsgp,
> -						 rpl_map, chl_map, ch_count,
> -						 byte_count);
> -	if (sge_count < 0) {
> -		err = -EIO;
> -		goto out;
> -	}
> -
> -	sgl_offset = 0;
> -	ch_no = 0;
> +	/* The request is completed when the RDMA_READs complete. The
> +	 * head context keeps all the pages that comprise the
> +	 * request.
> +	 */
> +	head->arg.head[0] = rqstp->rq_arg.head[0];
> +	head->arg.tail[0] = rqstp->rq_arg.tail[0];
> +	head->arg.pages = &head->pages[head->count];
> +	head->hdr_count = head->count;
> +	head->arg.page_base = 0;
> +	head->arg.page_len = 0;
> +	head->arg.len = rqstp->rq_arg.len;
> +	head->arg.buflen = rqstp->rq_arg.buflen + PAGE_SIZE;
> 
> +	page_no = 0; page_offset = 0;
> 	for (ch = (struct rpcrdma_read_chunk *)&rmsgp->rm_body.rm_chunks[0];
> -	     ch->rc_discrim != 0; ch++, ch_no++) {
> -		u64 rs_offset;
> -next_sge:
> -		ctxt = svc_rdma_get_context(xprt);
> -		ctxt->direction = DMA_FROM_DEVICE;
> -		ctxt->frmr = hdr_ctxt->frmr;
> -		ctxt->read_hdr = NULL;
> -		clear_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags);
> -		clear_bit(RDMACTXT_F_FAST_UNREG, &ctxt->flags);
> +	     ch->rc_discrim != 0; ch++) {


As I understand it, this loop is iterating over the items in the RPC
header’s read chunk list.

RFC 5667 section 4 says 

"The server MUST ignore any Read list for other NFS procedures, as well
as additional Read list entries beyond the first in the list."

But rdma_read_chunks() still expects multiple chunks in the incoming list.
Should this code follow the RFC and process only the first chunk in
each RPC header, or did I misunderstand the RFC text?

I’m not sure how the RPC layer should enforce the requirement to ignore
chunks for particular classes of NFS requests. But seems like valid
NFS/RDMA requests will have only zero or one item in each chunk list.


The ramification of this change:

The Linux client sends an extra chunk which is a zero pad to satisfy XDR
alignment. This results in an extra RDMA READ on the wire for a payload
that is never more than 3 bytes of zeros.

Section 3.7 of RFC 5666 states:

"If in turn, no data remains to be decoded from the inline portion, then
the receiver MUST conclude that roundup is present, and therefore it
advances the XDR decode position to that indicated by the next chunk (if
any).  In this way, roundup is passed without ever actually transferring
additional XDR bytes.”

Later, it states:

"Senders SHOULD therefore avoid encoding individual RDMA Read Chunks for
roundup whenever possible.”

The Solaris NFS/RDMA server does not require this extra chunk, but Linux
appears to need it. When I enable pad optimization on the Linux client,
it works fine with the Solaris server. But the first NFS WRITE with an
odd length against the Linux server causes connection loss and the client
workload hangs.

At some point I’d like to permanently enable this optimization on the
Linux client. You can try this out with:

 sudo echo 1 > /proc/sys/sunrpc/rdma_pad_optimize

The default contents of this file leave pad optimization disabled, for
compatibility with the current Linux NFS/RDMA server.

So rdma_read_chunks() needs to handle the implicit XDR length round-up.
That’s probably not hard.

What I’m asking is:

Do you agree the server should be changed to comply with section 4 of 5667?

Should you change now in this patch, or do you want me to write a patch
for it once the refactoring patch has been accepted?



> 
> -		/* Prepare READ WR */
> -		memset(&read_wr, 0, sizeof read_wr);
> -		read_wr.wr_id = (unsigned long)ctxt;
> -		read_wr.opcode = IB_WR_RDMA_READ;
> -		ctxt->wr_op = read_wr.opcode;
> -		read_wr.send_flags = IB_SEND_SIGNALED;
> -		read_wr.wr.rdma.rkey = ntohl(ch->rc_target.rs_handle);
> 		xdr_decode_hyper((__be32 *)&ch->rc_target.rs_offset,
> 				 &rs_offset);
> -		read_wr.wr.rdma.remote_addr = rs_offset + sgl_offset;
> -		read_wr.sg_list = ctxt->sge;
> -		read_wr.num_sge =
> -			rdma_read_max_sge(xprt, chl_map->ch[ch_no].count);
> -		err = rdma_set_ctxt_sge(xprt, ctxt, hdr_ctxt->frmr,
> -					&rpl_map->sge[chl_map->ch[ch_no].start],
> -					&sgl_offset,
> -					read_wr.num_sge);
> -		if (err) {
> -			svc_rdma_unmap_dma(ctxt);
> -			svc_rdma_put_context(ctxt, 0);
> -			goto out;
> -		}
> -		if (((ch+1)->rc_discrim == 0) &&
> -		    (read_wr.num_sge == chl_map->ch[ch_no].count)) {
> -			/*
> -			 * Mark the last RDMA_READ with a bit to
> -			 * indicate all RPC data has been fetched from
> -			 * the client and the RPC needs to be enqueued.
> -			 */
> -			set_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags);
> -			if (hdr_ctxt->frmr) {
> -				set_bit(RDMACTXT_F_FAST_UNREG, &ctxt->flags);
> -				/*
> -				 * Invalidate the local MR used to map the data
> -				 * sink.
> -				 */
> -				if (xprt->sc_dev_caps &
> -				    SVCRDMA_DEVCAP_READ_W_INV) {
> -					read_wr.opcode =
> -						IB_WR_RDMA_READ_WITH_INV;
> -					ctxt->wr_op = read_wr.opcode;
> -					read_wr.ex.invalidate_rkey =
> -						ctxt->frmr->mr->lkey;
> -				} else {
> -					/* Prepare INVALIDATE WR */
> -					memset(&inv_wr, 0, sizeof inv_wr);
> -					inv_wr.opcode = IB_WR_LOCAL_INV;
> -					inv_wr.send_flags = IB_SEND_SIGNALED;
> -					inv_wr.ex.invalidate_rkey =
> -						hdr_ctxt->frmr->mr->lkey;
> -					read_wr.next = &inv_wr;
> -				}
> -			}
> -			ctxt->read_hdr = hdr_ctxt;
> -		}
> -		/* Post the read */
> -		err = svc_rdma_send(xprt, &read_wr);
> -		if (err) {
> -			printk(KERN_ERR "svcrdma: Error %d posting RDMA_READ\n",
> -			       err);
> -			set_bit(XPT_CLOSE, &xprt->sc_xprt.xpt_flags);
> -			svc_rdma_unmap_dma(ctxt);
> -			svc_rdma_put_context(ctxt, 0);
> -			goto out;
> +		byte_count = ntohl(ch->rc_target.rs_length);
> +
> +		/* Use FRMR if supported */
> +		if (xprt->sc_dev_caps & SVCRDMA_DEVCAP_FAST_REG)
> +			reader = rdma_read_chunk_frmr;
> +		else
> +			reader = rdma_read_chunk_lcl;

The reader function is invariant across iterations of the for() loop.
In fact, it is invariant for all incoming requests on an xprt, isn’t it?

Can svc_rdma_create() plant that function pointer in the xprt?


> +		while (byte_count > 0) {
> +			ret = reader(xprt, rqstp, head,
> +				     &page_no, &page_offset,
> +				     ntohl(ch->rc_target.rs_handle),
> +				     byte_count, rs_offset,
> +				     ((ch+1)->rc_discrim == 0) /* last */
> +				     );
> +			if (ret < 0)
> +				goto err;
> +			byte_count -= ret;
> +			rs_offset += ret;
> 		}
> -		atomic_inc(&rdma_stat_read);
> -
> -		if (read_wr.num_sge < chl_map->ch[ch_no].count) {
> -			chl_map->ch[ch_no].count -= read_wr.num_sge;
> -			chl_map->ch[ch_no].start += read_wr.num_sge;
> -			goto next_sge;
> -		}
> -		sgl_offset = 0;
> -		err = 1;
> 	}
> -
> - out:
> -	svc_rdma_put_req_map(rpl_map);
> -	svc_rdma_put_req_map(chl_map);
> -
> +	ret = 1;
> + err:
> 	/* Detach arg pages. svc_recv will replenish them */
> -	for (ch_no = 0; &rqstp->rq_pages[ch_no] < rqstp->rq_respages; ch_no++)
> -		rqstp->rq_pages[ch_no] = NULL;
> +	for (page_no = 0;
> +	     &rqstp->rq_pages[page_no] < rqstp->rq_respages; page_no++)
> +		rqstp->rq_pages[page_no] = NULL;
> 
> -	return err;
> +	return ret;
> }
> 
> static int rdma_read_complete(struct svc_rqst *rqstp,
> @@ -595,13 +486,9 @@ int svc_rdma_recvfrom(struct svc_rqst *rqstp)
> 				  struct svc_rdma_op_ctxt,
> 				  dto_q);
> 		list_del_init(&ctxt->dto_q);
> -	}
> -	if (ctxt) {
> 		spin_unlock_bh(&rdma_xprt->sc_rq_dto_lock);
> 		return rdma_read_complete(rqstp, ctxt);
> -	}
> -
> -	if (!list_empty(&rdma_xprt->sc_rq_dto_q)) {
> +	} else if (!list_empty(&rdma_xprt->sc_rq_dto_q)) {
> 		ctxt = list_entry(rdma_xprt->sc_rq_dto_q.next,
> 				  struct svc_rdma_op_ctxt,
> 				  dto_q);
> @@ -621,7 +508,6 @@ int svc_rdma_recvfrom(struct svc_rqst *rqstp)
> 		if (test_bit(XPT_CLOSE, &xprt->xpt_flags))
> 			goto close_out;
> 
> -		BUG_ON(ret);
> 		goto out;
> 	}
> 	dprintk("svcrdma: processing ctxt=%p on xprt=%p, rqstp=%p, status=%d\n",
> @@ -644,12 +530,11 @@ int svc_rdma_recvfrom(struct svc_rqst *rqstp)
> 	}
> 
> 	/* Read read-list data. */
> -	ret = rdma_read_xdr(rdma_xprt, rmsgp, rqstp, ctxt);
> +	ret = rdma_read_chunks(rdma_xprt, rmsgp, rqstp, ctxt);
> 	if (ret > 0) {
> 		/* read-list posted, defer until data received from client. */
> 		goto defer;
> -	}
> -	if (ret < 0) {
> +	} else if (ret < 0) {
> 		/* Post of read-list failed, free context. */
> 		svc_rdma_put_context(ctxt, 1);
> 		return 0;
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-rdma" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

--
Chuck Lever
chucklever@gmail.com



--
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Steve Wise May 13, 2014, 8:37 p.m. UTC | #2

> -----Original Message-----
> From: Chuck Lever [mailto:chucklever@gmail.com]
> Sent: Tuesday, May 13, 2014 1:22 PM
> To: Steve Wise
> Cc: J. Bruce Fields; Linux NFS Mailing List; linux-rdma@vger.kernel.org; Tom Tucker
> Subject: Re: [PATCH V2 RFC 2/3] svcrdma: Recvfrom changes
> 
> Hi Steve-
> 
> Some random review comments, see below.
> 

<snip>

> > +static int rdma_read_chunks(struct svcxprt_rdma *xprt,
> > +			    struct rpcrdma_msg *rmsgp,
> > +			    struct svc_rqst *rqstp,
> > +			    struct svc_rdma_op_ctxt *head)
> > {
> > -	struct ib_send_wr read_wr;
> > -	struct ib_send_wr inv_wr;
> > -	int err = 0;
> > -	int ch_no;
> > -	int ch_count;
> > -	int byte_count;
> > -	int sge_count;
> > -	u64 sgl_offset;
> > +	int page_no, ch_count, ret;
> > 	struct rpcrdma_read_chunk *ch;
> > -	struct svc_rdma_op_ctxt *ctxt = NULL;
> > -	struct svc_rdma_req_map *rpl_map;
> > -	struct svc_rdma_req_map *chl_map;
> > +	u32 page_offset, byte_count;
> > +	u64 rs_offset;
> > +	rdma_reader_fn reader;
> >
> > 	/* If no read list is present, return 0 */
> > 	ch = svc_rdma_get_read_chunk(rmsgp);
> > @@ -408,122 +368,53 @@ static int rdma_read_xdr(struct svcxprt_rdma *xprt,
> > 	if (ch_count > RPCSVC_MAXPAGES)
> > 		return -EINVAL;
> 
> I'm not sure what this ^^^ ch_count check is doing, but maybe I haven't had
> enough caffeine this morning. Shouldn't this code be comparing the segment
> count, not the chunk count, with MAXPAGES?

Isn't ch_count really the number of chunks in the RPC?  I'm not sure what "segment count"
you are talking about?

> 
> 
> >
> > -	/* Allocate temporary reply and chunk maps */
> > -	rpl_map = svc_rdma_get_req_map();
> > -	chl_map = svc_rdma_get_req_map();
> > -
> > -	if (!xprt->sc_frmr_pg_list_len)
> > -		sge_count = map_read_chunks(xprt, rqstp, hdr_ctxt, rmsgp,
> > -					    rpl_map, chl_map, ch_count,
> > -					    byte_count);
> > -	else
> > -		sge_count = fast_reg_read_chunks(xprt, rqstp, hdr_ctxt, rmsgp,
> > -						 rpl_map, chl_map, ch_count,
> > -						 byte_count);
> > -	if (sge_count < 0) {
> > -		err = -EIO;
> > -		goto out;
> > -	}
> > -
> > -	sgl_offset = 0;
> > -	ch_no = 0;
> > +	/* The request is completed when the RDMA_READs complete. The
> > +	 * head context keeps all the pages that comprise the
> > +	 * request.
> > +	 */
> > +	head->arg.head[0] = rqstp->rq_arg.head[0];
> > +	head->arg.tail[0] = rqstp->rq_arg.tail[0];
> > +	head->arg.pages = &head->pages[head->count];
> > +	head->hdr_count = head->count;
> > +	head->arg.page_base = 0;
> > +	head->arg.page_len = 0;
> > +	head->arg.len = rqstp->rq_arg.len;
> > +	head->arg.buflen = rqstp->rq_arg.buflen + PAGE_SIZE;
> >
> > +	page_no = 0; page_offset = 0;
> > 	for (ch = (struct rpcrdma_read_chunk *)&rmsgp->rm_body.rm_chunks[0];
> > -	     ch->rc_discrim != 0; ch++, ch_no++) {
> > -		u64 rs_offset;
> > -next_sge:
> > -		ctxt = svc_rdma_get_context(xprt);
> > -		ctxt->direction = DMA_FROM_DEVICE;
> > -		ctxt->frmr = hdr_ctxt->frmr;
> > -		ctxt->read_hdr = NULL;
> > -		clear_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags);
> > -		clear_bit(RDMACTXT_F_FAST_UNREG, &ctxt->flags);
> > +	     ch->rc_discrim != 0; ch++) {
> 
> 
> As I understand it, this loop is iterating over the items in the RPC
> header's read chunk list.
> 
> RFC 5667 section 4 says
> 
> "The server MUST ignore any Read list for other NFS procedures, as well
> as additional Read list entries beyond the first in the list."
> 

I interpret this to say the server should ignore an RDMA Write list, if present, when
processing an NFS WRITE (because the server emits RDMA Reads to the client in this case).
Similarly, it should ignore an RDMA Read list when processing an NFS READ (which generates
RDMA Writes from the server->client to fulfill the NFS READ). 

> But rdma_read_chunks() still expects multiple chunks in the incoming list.

An RDMA Read list can have multiple chunks, yes?


> Should this code follow the RFC and process only the first chunk in
> each RPC header, or did I misunderstand the RFC text?
> 
> I'm not sure how the RPC layer should enforce the requirement to ignore
> chunks for particular classes of NFS requests. But seems like valid
> NFS/RDMA requests will have only zero or one item in each chunk list.
> 
> 
> The ramification of this change:
> 
> The Linux client sends an extra chunk which is a zero pad to satisfy XDR
> alignment. This results in an extra RDMA READ on the wire for a payload
> that is never more than 3 bytes of zeros.
>

This sounds like a logic bug in the server then.  You see these IOs on the wire?
 
> Section 3.7 of RFC 5666 states:
> 
> "If in turn, no data remains to be decoded from the inline portion, then
> the receiver MUST conclude that roundup is present, and therefore it
> advances the XDR decode position to that indicated by the next chunk (if
> any).  In this way, roundup is passed without ever actually transferring
> additional XDR bytes."
> 
> Later, it states:
> 
> "Senders SHOULD therefore avoid encoding individual RDMA Read Chunks for
> roundup whenever possible."
> 
> The Solaris NFS/RDMA server does not require this extra chunk, but Linux
> appears to need it. When I enable pad optimization on the Linux client,
> it works fine with the Solaris server. But the first NFS WRITE with an
> odd length against the Linux server causes connection loss and the client
> workload hangs.
> 
> At some point I'd like to permanently enable this optimization on the
> Linux client. You can try this out with:
> 
>  sudo echo 1 > /proc/sys/sunrpc/rdma_pad_optimize
> 
> The default contents of this file leave pad optimization disabled, for
> compatibility with the current Linux NFS/RDMA server.
> 
> So rdma_read_chunks() needs to handle the implicit XDR length round-up.
> That's probably not hard.
> 
> What I'm asking is:
> 
> Do you agree the server should be changed to comply with section 4 of 5667?
> 

I think it is complying and you are misinterpreting.  But I could be misinterpreting it
too :)

But we should fix the pad thing.

> Should you change now in this patch, or do you want me to write a patch
> for it once the refactoring patch has been accepted?
> 

I'd like to get this refactoring in and then continue improving it.  Unfortunately, I
think you still see some bug running over mthca, eh?  I haven't debugged that yet.  I plan
to and then resubmit V3 (squashed).


> 
> 
> >
> > -		/* Prepare READ WR */
> > -		memset(&read_wr, 0, sizeof read_wr);
> > -		read_wr.wr_id = (unsigned long)ctxt;
> > -		read_wr.opcode = IB_WR_RDMA_READ;
> > -		ctxt->wr_op = read_wr.opcode;
> > -		read_wr.send_flags = IB_SEND_SIGNALED;
> > -		read_wr.wr.rdma.rkey = ntohl(ch->rc_target.rs_handle);
> > 		xdr_decode_hyper((__be32 *)&ch->rc_target.rs_offset,
> > 				 &rs_offset);
> > -		read_wr.wr.rdma.remote_addr = rs_offset + sgl_offset;
> > -		read_wr.sg_list = ctxt->sge;
> > -		read_wr.num_sge =
> > -			rdma_read_max_sge(xprt, chl_map->ch[ch_no].count);
> > -		err = rdma_set_ctxt_sge(xprt, ctxt, hdr_ctxt->frmr,
> > -					&rpl_map->sge[chl_map->ch[ch_no].start],
> > -					&sgl_offset,
> > -					read_wr.num_sge);
> > -		if (err) {
> > -			svc_rdma_unmap_dma(ctxt);
> > -			svc_rdma_put_context(ctxt, 0);
> > -			goto out;
> > -		}
> > -		if (((ch+1)->rc_discrim == 0) &&
> > -		    (read_wr.num_sge == chl_map->ch[ch_no].count)) {
> > -			/*
> > -			 * Mark the last RDMA_READ with a bit to
> > -			 * indicate all RPC data has been fetched from
> > -			 * the client and the RPC needs to be enqueued.
> > -			 */
> > -			set_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags);
> > -			if (hdr_ctxt->frmr) {
> > -				set_bit(RDMACTXT_F_FAST_UNREG, &ctxt->flags);
> > -				/*
> > -				 * Invalidate the local MR used to map the data
> > -				 * sink.
> > -				 */
> > -				if (xprt->sc_dev_caps &
> > -				    SVCRDMA_DEVCAP_READ_W_INV) {
> > -					read_wr.opcode =
> > -						IB_WR_RDMA_READ_WITH_INV;
> > -					ctxt->wr_op = read_wr.opcode;
> > -					read_wr.ex.invalidate_rkey =
> > -						ctxt->frmr->mr->lkey;
> > -				} else {
> > -					/* Prepare INVALIDATE WR */
> > -					memset(&inv_wr, 0, sizeof inv_wr);
> > -					inv_wr.opcode = IB_WR_LOCAL_INV;
> > -					inv_wr.send_flags = IB_SEND_SIGNALED;
> > -					inv_wr.ex.invalidate_rkey =
> > -						hdr_ctxt->frmr->mr->lkey;
> > -					read_wr.next = &inv_wr;
> > -				}
> > -			}
> > -			ctxt->read_hdr = hdr_ctxt;
> > -		}
> > -		/* Post the read */
> > -		err = svc_rdma_send(xprt, &read_wr);
> > -		if (err) {
> > -			printk(KERN_ERR "svcrdma: Error %d posting RDMA_READ\n",
> > -			       err);
> > -			set_bit(XPT_CLOSE, &xprt->sc_xprt.xpt_flags);
> > -			svc_rdma_unmap_dma(ctxt);
> > -			svc_rdma_put_context(ctxt, 0);
> > -			goto out;
> > +		byte_count = ntohl(ch->rc_target.rs_length);
> > +
> > +		/* Use FRMR if supported */
> > +		if (xprt->sc_dev_caps & SVCRDMA_DEVCAP_FAST_REG)
> > +			reader = rdma_read_chunk_frmr;
> > +		else
> > +			reader = rdma_read_chunk_lcl;
> 
> The reader function is invariant across iterations of the for() loop.
> In fact, it is invariant for all incoming requests on an xprt, isn't it?
> 
> Can svc_rdma_create() plant that function pointer in the xprt?
> 

Yea, that sounds good. 


Thanks for reviewing!

Steve.

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Chuck Lever May 13, 2014, 9:44 p.m. UTC | #3

On May 13, 2014, at 4:37 PM, Steve Wise <swise@opengridcomputing.com> wrote:

> 
> 
>> -----Original Message-----
>> From: Chuck Lever [mailto:chucklever@gmail.com]
>> Sent: Tuesday, May 13, 2014 1:22 PM
>> To: Steve Wise
>> Cc: J. Bruce Fields; Linux NFS Mailing List; linux-rdma@vger.kernel.org; Tom Tucker
>> Subject: Re: [PATCH V2 RFC 2/3] svcrdma: Recvfrom changes
>> 
>> Hi Steve-
>> 
>> Some random review comments, see below.
>> 
> 
> <snip>
> 
>>> +static int rdma_read_chunks(struct svcxprt_rdma *xprt,
>>> +			    struct rpcrdma_msg *rmsgp,
>>> +			    struct svc_rqst *rqstp,
>>> +			    struct svc_rdma_op_ctxt *head)
>>> {
>>> -	struct ib_send_wr read_wr;
>>> -	struct ib_send_wr inv_wr;
>>> -	int err = 0;
>>> -	int ch_no;
>>> -	int ch_count;
>>> -	int byte_count;
>>> -	int sge_count;
>>> -	u64 sgl_offset;
>>> +	int page_no, ch_count, ret;
>>> 	struct rpcrdma_read_chunk *ch;
>>> -	struct svc_rdma_op_ctxt *ctxt = NULL;
>>> -	struct svc_rdma_req_map *rpl_map;
>>> -	struct svc_rdma_req_map *chl_map;
>>> +	u32 page_offset, byte_count;
>>> +	u64 rs_offset;
>>> +	rdma_reader_fn reader;
>>> 
>>> 	/* If no read list is present, return 0 */
>>> 	ch = svc_rdma_get_read_chunk(rmsgp);
>>> @@ -408,122 +368,53 @@ static int rdma_read_xdr(struct svcxprt_rdma *xprt,
>>> 	if (ch_count > RPCSVC_MAXPAGES)
>>> 		return -EINVAL;
>> 
>> I'm not sure what this ^^^ ch_count check is doing, but maybe I haven't had
>> enough caffeine this morning. Shouldn't this code be comparing the segment
>> count, not the chunk count, with MAXPAGES?
> 
> Isn't ch_count really the number of chunks in the RPC?

Sort of. Block comment in front of svc_rdma_rcl_chunk_counts() reads:

 74  * Determine number of chunks and total bytes in chunk list. The chunk
 75  * list has already been verified to fit within the RPCRDMA header.

So, called from rdma_read_chunks(), ch_count is the number of chunks in
the Read list.

As you point out below, NFS/RDMA passes either a Read or a Write list,
not both. So it amounts to the same thing as the total number of chunks
in the RPC.

> I'm not sure what "segment count” you are talking about?

AFAICT a chunk is a list of segments. Thus one chunk can reference
many pages, one per segment.

If you print ch_count, it is 2 for NFS WRITEs from a Linux client,
no matter how large the write payload is. Therefore I think the check
as it is written is not particularly useful.

The returned ch_count here is not used beyond that check, after the
refactoring patch is applied. The returned byte_count includes all
chunks in the passed-in chunk list, whereas I think it should count
only the first chunk in the list.

> 
>> 
>> 
>>> 
>>> -	/* Allocate temporary reply and chunk maps */
>>> -	rpl_map = svc_rdma_get_req_map();
>>> -	chl_map = svc_rdma_get_req_map();
>>> -
>>> -	if (!xprt->sc_frmr_pg_list_len)
>>> -		sge_count = map_read_chunks(xprt, rqstp, hdr_ctxt, rmsgp,
>>> -					    rpl_map, chl_map, ch_count,
>>> -					    byte_count);
>>> -	else
>>> -		sge_count = fast_reg_read_chunks(xprt, rqstp, hdr_ctxt, rmsgp,
>>> -						 rpl_map, chl_map, ch_count,
>>> -						 byte_count);
>>> -	if (sge_count < 0) {
>>> -		err = -EIO;
>>> -		goto out;
>>> -	}
>>> -
>>> -	sgl_offset = 0;
>>> -	ch_no = 0;
>>> +	/* The request is completed when the RDMA_READs complete. The
>>> +	 * head context keeps all the pages that comprise the
>>> +	 * request.
>>> +	 */
>>> +	head->arg.head[0] = rqstp->rq_arg.head[0];
>>> +	head->arg.tail[0] = rqstp->rq_arg.tail[0];
>>> +	head->arg.pages = &head->pages[head->count];
>>> +	head->hdr_count = head->count;
>>> +	head->arg.page_base = 0;
>>> +	head->arg.page_len = 0;
>>> +	head->arg.len = rqstp->rq_arg.len;
>>> +	head->arg.buflen = rqstp->rq_arg.buflen + PAGE_SIZE;
>>> 
>>> +	page_no = 0; page_offset = 0;
>>> 	for (ch = (struct rpcrdma_read_chunk *)&rmsgp->rm_body.rm_chunks[0];
>>> -	     ch->rc_discrim != 0; ch++, ch_no++) {
>>> -		u64 rs_offset;
>>> -next_sge:
>>> -		ctxt = svc_rdma_get_context(xprt);
>>> -		ctxt->direction = DMA_FROM_DEVICE;
>>> -		ctxt->frmr = hdr_ctxt->frmr;
>>> -		ctxt->read_hdr = NULL;
>>> -		clear_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags);
>>> -		clear_bit(RDMACTXT_F_FAST_UNREG, &ctxt->flags);
>>> +	     ch->rc_discrim != 0; ch++) {
>> 
>> 
>> As I understand it, this loop is iterating over the items in the RPC
>> header's read chunk list.
>> 
>> RFC 5667 section 4 says
>> 
>> "The server MUST ignore any Read list for other NFS procedures, as well
>> as additional Read list entries beyond the first in the list."
>> 
> 
> I interpret this to say the server should ignore an RDMA Write list, if present, when
> processing an NFS WRITE (because the server emits RDMA Reads to the client in this case).
> Similarly, it should ignore an RDMA Read list when processing an NFS READ (which generates
> RDMA Writes from the server->client to fulfill the NFS READ). 

That’s already stated explicitly in a later paragraph. So this text
is getting at something else, IMO. Here’s the full context:

4.  NFS Versions 2 and 3 Mapping

   A single RDMA Write list entry MAY be posted by the client to receive
   either the opaque file data from a READ request or the pathname from
   a READLINK request.  The server MUST ignore a Write list for any
   other NFS procedure, as well as any Write list entries beyond the
   first in the list.

   Similarly, a single RDMA Read list entry MAY be posted by the client
   to supply the opaque file data for a WRITE request or the pathname
   for a SYMLINK request.  The server MUST ignore any Read list for
   other NFS procedures, as well as additional Read list entries beyond
   the first in the list.

   Because there are no NFS version 2 or 3 requests that transfer bulk
   data in both directions, it is not necessary to post requests
   containing both Write and Read lists.  Any unneeded Read or Write
   lists are ignored by the server.

If there is a Read list, it can contain one chunk for NFS WRITE and
SYMLINK operations, otherwise it should contain zero chunks. Anything
else MUST be ignored (ie, the server mustn’t process the additional
chunks, and mustn’t throw an error).

Processing the second chunk from the client during NFS WRITE operations
is incorrect. The additional chunk should be ignored, and the first
chunk should be padded on the server to make things work right in the
upper layer (the server’s NFS WRITE XDR decoder).

> 
>> But rdma_read_chunks() still expects multiple chunks in the incoming list.
> 
> An RDMA Read list can have multiple chunks, yes?

It can. But RFC 5667 suggests that particularly for NFS requests, only
a Read list of zero or one chunks is valid.

> 
>> Should this code follow the RFC and process only the first chunk in
>> each RPC header, or did I misunderstand the RFC text?
>> 
>> I'm not sure how the RPC layer should enforce the requirement to ignore
>> chunks for particular classes of NFS requests. But seems like valid
>> NFS/RDMA requests will have only zero or one item in each chunk list.
>> 
>> 
>> The ramification of this change:
>> 
>> The Linux client sends an extra chunk which is a zero pad to satisfy XDR
>> alignment. This results in an extra RDMA READ on the wire for a payload
>> that is never more than 3 bytes of zeros.
>> 
> 
> This sounds like a logic bug in the server then.

Perhaps it’s simply that this code was designed before RFC 5667 was
published. Certainly the client expects the server might work this way.

> You see these IOs on the wire?

I see extra iterations in the RDMA READ loop on the server, both before
and after the refactoring patch.

I haven’t looked at the wire because ib_dump doesn’t work with the mthca
provider.

> 
>> Section 3.7 of RFC 5666 states:
>> 
>> "If in turn, no data remains to be decoded from the inline portion, then
>> the receiver MUST conclude that roundup is present, and therefore it
>> advances the XDR decode position to that indicated by the next chunk (if
>> any).  In this way, roundup is passed without ever actually transferring
>> additional XDR bytes."
>> 
>> Later, it states:
>> 
>> "Senders SHOULD therefore avoid encoding individual RDMA Read Chunks for
>> roundup whenever possible."
>> 
>> The Solaris NFS/RDMA server does not require this extra chunk, but Linux
>> appears to need it. When I enable pad optimization on the Linux client,
>> it works fine with the Solaris server. But the first NFS WRITE with an
>> odd length against the Linux server causes connection loss and the client
>> workload hangs.
>> 
>> At some point I'd like to permanently enable this optimization on the
>> Linux client. You can try this out with:
>> 
>> sudo echo 1 > /proc/sys/sunrpc/rdma_pad_optimize
>> 
>> The default contents of this file leave pad optimization disabled, for
>> compatibility with the current Linux NFS/RDMA server.
>> 
>> So rdma_read_chunks() needs to handle the implicit XDR length round-up.
>> That's probably not hard.
>> 
>> What I'm asking is:
>> 
>> Do you agree the server should be changed to comply with section 4 of 5667?
>> 
> 
> I think it is complying and you are misinterpreting.  But I could be misinterpreting it
> too :)
> 
> But we should fix the pad thing.

That may be enough to support a client that does not send the
pad bytes in a separate chunk. However, I wonder how such a
server would behave with the current client.

True, this isn’t a regression, per se. The server is already
behaving incorrectly without the refactoring patch.

However, Tom’s refactoring rewrites all this logic anyway, and
it wouldn’t be much of a stretch to make the server comply with
RFC 5667, at this point.

--
Chuck Lever
chucklever@gmail.com

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Steve Wise May 14, 2014, 2:26 p.m. UTC | #4

On 5/13/2014 4:44 PM, Chuck Lever wrote:
>>>> +static int rdma_read_chunks(struct svcxprt_rdma *xprt,
>>>> +			    struct rpcrdma_msg *rmsgp,
>>>> +			    struct svc_rqst *rqstp,
>>>> +			    struct svc_rdma_op_ctxt *head)
>>>> {
>>>> -	struct ib_send_wr read_wr;
>>>> -	struct ib_send_wr inv_wr;
>>>> -	int err = 0;
>>>> -	int ch_no;
>>>> -	int ch_count;
>>>> -	int byte_count;
>>>> -	int sge_count;
>>>> -	u64 sgl_offset;
>>>> +	int page_no, ch_count, ret;
>>>> 	struct rpcrdma_read_chunk *ch;
>>>> -	struct svc_rdma_op_ctxt *ctxt = NULL;
>>>> -	struct svc_rdma_req_map *rpl_map;
>>>> -	struct svc_rdma_req_map *chl_map;
>>>> +	u32 page_offset, byte_count;
>>>> +	u64 rs_offset;
>>>> +	rdma_reader_fn reader;
>>>>
>>>> 	/* If no read list is present, return 0 */
>>>> 	ch = svc_rdma_get_read_chunk(rmsgp);
>>>> @@ -408,122 +368,53 @@ static int rdma_read_xdr(struct svcxprt_rdma *xprt,
>>>> 	if (ch_count > RPCSVC_MAXPAGES)
>>>> 		return -EINVAL;
>>> I'm not sure what this ^^^ ch_count check is doing, but maybe I haven't had
>>> enough caffeine this morning. Shouldn't this code be comparing the segment
>>> count, not the chunk count, with MAXPAGES?
>> Isn't ch_count really the number of chunks in the RPC?
> Sort of. Block comment in front of svc_rdma_rcl_chunk_counts() reads:
>
>   74  * Determine number of chunks and total bytes in chunk list. The chunk
>   75  * list has already been verified to fit within the RPCRDMA header.
>
> So, called from rdma_read_chunks(), ch_count is the number of chunks in
> the Read list.
>
> As you point out below, NFS/RDMA passes either a Read or a Write list,
> not both. So it amounts to the same thing as the total number of chunks
> in the RPC.
>
>> I'm not sure what "segment count” you are talking about?
> AFAICT a chunk is a list of segments. Thus one chunk can reference
> many pages, one per segment.

Ok yes.  rdma_read_chunk_frmr()/rdma_read_chunk_lcl() walk the segments 
creating rdma read work requests to pull the data for this chunk.

> If you print ch_count, it is 2 for NFS WRITEs from a Linux client,
> no matter how large the write payload is. Therefore I think the check
> as it is written is not particularly useful.

Why are there 2?

> The returned ch_count here is not used beyond that check, after the
> refactoring patch is applied. The returned byte_count includes all
> chunks in the passed-in chunk list, whereas I think it should count
> only the first chunk in the list.

So I'll investigate this more with the goal of only grabbing the first 
chunk.

>>>
>>>> -	/* Allocate temporary reply and chunk maps */
>>>> -	rpl_map = svc_rdma_get_req_map();
>>>> -	chl_map = svc_rdma_get_req_map();
>>>> -
>>>> -	if (!xprt->sc_frmr_pg_list_len)
>>>> -		sge_count = map_read_chunks(xprt, rqstp, hdr_ctxt, rmsgp,
>>>> -					    rpl_map, chl_map, ch_count,
>>>> -					    byte_count);
>>>> -	else
>>>> -		sge_count = fast_reg_read_chunks(xprt, rqstp, hdr_ctxt, rmsgp,
>>>> -						 rpl_map, chl_map, ch_count,
>>>> -						 byte_count);
>>>> -	if (sge_count < 0) {
>>>> -		err = -EIO;
>>>> -		goto out;
>>>> -	}
>>>> -
>>>> -	sgl_offset = 0;
>>>> -	ch_no = 0;
>>>> +	/* The request is completed when the RDMA_READs complete. The
>>>> +	 * head context keeps all the pages that comprise the
>>>> +	 * request.
>>>> +	 */
>>>> +	head->arg.head[0] = rqstp->rq_arg.head[0];
>>>> +	head->arg.tail[0] = rqstp->rq_arg.tail[0];
>>>> +	head->arg.pages = &head->pages[head->count];
>>>> +	head->hdr_count = head->count;
>>>> +	head->arg.page_base = 0;
>>>> +	head->arg.page_len = 0;
>>>> +	head->arg.len = rqstp->rq_arg.len;
>>>> +	head->arg.buflen = rqstp->rq_arg.buflen + PAGE_SIZE;
>>>>
>>>> +	page_no = 0; page_offset = 0;
>>>> 	for (ch = (struct rpcrdma_read_chunk *)&rmsgp->rm_body.rm_chunks[0];
>>>> -	     ch->rc_discrim != 0; ch++, ch_no++) {
>>>> -		u64 rs_offset;
>>>> -next_sge:
>>>> -		ctxt = svc_rdma_get_context(xprt);
>>>> -		ctxt->direction = DMA_FROM_DEVICE;
>>>> -		ctxt->frmr = hdr_ctxt->frmr;
>>>> -		ctxt->read_hdr = NULL;
>>>> -		clear_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags);
>>>> -		clear_bit(RDMACTXT_F_FAST_UNREG, &ctxt->flags);
>>>> +	     ch->rc_discrim != 0; ch++) {
>>>
>>> As I understand it, this loop is iterating over the items in the RPC
>>> header's read chunk list.
>>>
>>> RFC 5667 section 4 says
>>>
>>> "The server MUST ignore any Read list for other NFS procedures, as well
>>> as additional Read list entries beyond the first in the list."
>>>
>> I interpret this to say the server should ignore an RDMA Write list, if present, when
>> processing an NFS WRITE (because the server emits RDMA Reads to the client in this case).
>> Similarly, it should ignore an RDMA Read list when processing an NFS READ (which generates
>> RDMA Writes from the server->client to fulfill the NFS READ).
> That’s already stated explicitly in a later paragraph. So this text
> is getting at something else, IMO. Here’s the full context:
>   
> 4.  NFS Versions 2 and 3 Mapping
>
>     A single RDMA Write list entry MAY be posted by the client to receive
>     either the opaque file data from a READ request or the pathname from
>     a READLINK request.  The server MUST ignore a Write list for any
>     other NFS procedure, as well as any Write list entries beyond the
>     first in the list.
>
>     Similarly, a single RDMA Read list entry MAY be posted by the client
>     to supply the opaque file data for a WRITE request or the pathname
>     for a SYMLINK request.  The server MUST ignore any Read list for
>     other NFS procedures, as well as additional Read list entries beyond
>     the first in the list.
>
>     Because there are no NFS version 2 or 3 requests that transfer bulk
>     data in both directions, it is not necessary to post requests
>     containing both Write and Read lists.  Any unneeded Read or Write
>     lists are ignored by the server.
>
> If there is a Read list, it can contain one chunk for NFS WRITE and
> SYMLINK operations, otherwise it should contain zero chunks. Anything
> else MUST be ignored (ie, the server mustn’t process the additional
> chunks, and mustn’t throw an error).
>
> Processing the second chunk from the client during NFS WRITE operations
> is incorrect. The additional chunk should be ignored, and the first
> chunk should be padded on the server to make things work right in the
> upper layer (the server’s NFS WRITE XDR decoder).

Ok.  Padding is another issue, and I'd like to defer it until we get 
this refactor patch merged.

>
>>> But rdma_read_chunks() still expects multiple chunks in the incoming list.
>> An RDMA Read list can have multiple chunks, yes?
> It can. But RFC 5667 suggests that particularly for NFS requests, only
> a Read list of zero or one chunks is valid.
>
>>> Should this code follow the RFC and process only the first chunk in
>>> each RPC header, or did I misunderstand the RFC text?
>>>
>>> I'm not sure how the RPC layer should enforce the requirement to ignore
>>> chunks for particular classes of NFS requests. But seems like valid
>>> NFS/RDMA requests will have only zero or one item in each chunk list.
>>>
>>>
>>> The ramification of this change:
>>>
>>> The Linux client sends an extra chunk which is a zero pad to satisfy XDR
>>> alignment. This results in an extra RDMA READ on the wire for a payload
>>> that is never more than 3 bytes of zeros.
>>>
>> This sounds like a logic bug in the server then.
> Perhaps it’s simply that this code was designed before RFC 5667 was
> published. Certainly the client expects the server might work this way.

I don't think so.  Just never implemented correctly.

>> You see these IOs on the wire?
> I see extra iterations in the RDMA READ loop on the server, both before
> and after the refactoring patch.
>
> I haven’t looked at the wire because ib_dump doesn’t work with the mthca
> provider.
>
>>> Section 3.7 of RFC 5666 states:
>>>
>>> "If in turn, no data remains to be decoded from the inline portion, then
>>> the receiver MUST conclude that roundup is present, and therefore it
>>> advances the XDR decode position to that indicated by the next chunk (if
>>> any).  In this way, roundup is passed without ever actually transferring
>>> additional XDR bytes."
>>>
>>> Later, it states:
>>>
>>> "Senders SHOULD therefore avoid encoding individual RDMA Read Chunks for
>>> roundup whenever possible."
>>>
>>> The Solaris NFS/RDMA server does not require this extra chunk, but Linux
>>> appears to need it. When I enable pad optimization on the Linux client,
>>> it works fine with the Solaris server. But the first NFS WRITE with an
>>> odd length against the Linux server causes connection loss and the client
>>> workload hangs.
>>>
>>> At some point I'd like to permanently enable this optimization on the
>>> Linux client. You can try this out with:
>>>
>>> sudo echo 1 > /proc/sys/sunrpc/rdma_pad_optimize
>>>
>>> The default contents of this file leave pad optimization disabled, for
>>> compatibility with the current Linux NFS/RDMA server.
>>>
>>> So rdma_read_chunks() needs to handle the implicit XDR length round-up.
>>> That's probably not hard.
>>>
>>> What I'm asking is:
>>>
>>> Do you agree the server should be changed to comply with section 4 of 5667?
>>>
>> I think it is complying and you are misinterpreting.  But I could be misinterpreting it
>> too :)
>>
>> But we should fix the pad thing.
> That may be enough to support a client that does not send the
> pad bytes in a separate chunk. However, I wonder how such a
> server would behave with the current client.
>
> True, this isn’t a regression, per se. The server is already
> behaving incorrectly without the refactoring patch.
>
> However, Tom’s refactoring rewrites all this logic anyway, and
> it wouldn’t be much of a stretch to make the server comply with
> RFC 5667, at this point.

Can we defer this until the refactor patch is in, then I'll work on a 
new patch for the pad stuff.

Thanks,

Steve.
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Chuck Lever May 14, 2014, 2:39 p.m. UTC | #5

On May 14, 2014, at 10:26 AM, Steve Wise <swise@opengridcomputing.com> wrote:

> On 5/13/2014 4:44 PM, Chuck Lever wrote:
>> 
>>> I'm not sure what "segment count” you are talking about?
>> AFAICT a chunk is a list of segments. Thus one chunk can reference
>> many pages, one per segment.
> 
> Ok yes.  rdma_read_chunk_frmr()/rdma_read_chunk_lcl() walk the segments creating rdma read work requests to pull the data for this chunk.
> 
>> If you print ch_count, it is 2 for NFS WRITEs from a Linux client,
>> no matter how large the write payload is. Therefore I think the check
>> as it is written is not particularly useful.
> 
> Why are there 2?

The first chunk lists the pages the server is to read, and the second
chunk has the zero pad for XDR alignment.

If pad optimization is enabled on the client, there is just 1 chunk in
the RPC’s Read list.

> 
>> The returned ch_count here is not used beyond that check, after the
>> refactoring patch is applied. The returned byte_count includes all
>> chunks in the passed-in chunk list, whereas I think it should count
>> only the first chunk in the list.
> 
> So I'll investigate this more with the goal of only grabbing the first chunk.

[ . . . snipped . . . ]

>>>> 
>>>> What I'm asking is:
>>>> 
>>>> Do you agree the server should be changed to comply with section 4 of 5667?
>>>> 
>>> I think it is complying and you are misinterpreting.  But I could be misinterpreting it
>>> too :)
>>> 
>>> But we should fix the pad thing.
>> That may be enough to support a client that does not send the
>> pad bytes in a separate chunk. However, I wonder how such a
>> server would behave with the current client.
>> 
>> True, this isn’t a regression, per se. The server is already
>> behaving incorrectly without the refactoring patch.
>> 
>> However, Tom’s refactoring rewrites all this logic anyway, and
>> it wouldn’t be much of a stretch to make the server comply with
>> RFC 5667, at this point.
> 
> Can we defer this until the refactor patch is in, then I'll work on a new patch for the pad stuff.

Yes, we can defer it.

A bug has been filed to track this issue:

 https://bugzilla.linux-nfs.org/show_bug.cgi?id=246

--
Chuck Lever
chucklever@gmail.com



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Steve Wise May 14, 2014, 6:11 p.m. UTC | #6

> >
> >> If you print ch_count, it is 2 for NFS WRITEs from a Linux client,
> >> no matter how large the write payload is. Therefore I think the check
> >> as it is written is not particularly useful.
> >
> > Why are there 2?
> 
> The first chunk lists the pages the server is to read, and the second
> chunk has the zero pad for XDR alignment.
> 
> If pad optimization is enabled on the client, there is just 1 chunk in
> the RPC's Read list.
> 

So the code as it stands violates the RFC by sending 2 chunks?  And if I change the server
to only consume 1, then everything unaligned will break?



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Chuck Lever May 14, 2014, 6:21 p.m. UTC | #7

On May 14, 2014, at 2:11 PM, Steve Wise <swise@opengridcomputing.com> wrote:

> 
>>> 
>>>> If you print ch_count, it is 2 for NFS WRITEs from a Linux client,
>>>> no matter how large the write payload is. Therefore I think the check
>>>> as it is written is not particularly useful.
>>> 
>>> Why are there 2?
>> 
>> The first chunk lists the pages the server is to read, and the second
>> chunk has the zero pad for XDR alignment.
>> 
>> If pad optimization is enabled on the client, there is just 1 chunk in
>> the RPC's Read list.
>> 
> 
> So the code as it stands violates the RFC by sending 2 chunks?

The Linux client is non-compliant because it sends two chunks. A compliant server ignores the second chunk, so this is functionally harmless (but a waste of resources).

The Linux server is non-compliant because it _requires_ the XDR pad chunk. A compliant client (eg. Linux with pad optimization enabled) does not interoperate with it.

> And if I change the server
> to only consume 1, then everything unaligned will break?

If you change the server to consume only the first chunk, but do not also make it deal with XDR padding as recommended in chapter 3 of RFC 5666, then WRITEs with a length that is not a multiple of four will fail. SYMLINKs with a large payload will also have this problem.

--
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chucklever@gmail.com

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Steve Wise May 14, 2014, 6:24 p.m. UTC | #8

> >>
> >
> > So the code as it stands violates the RFC by sending 2 chunks?
> 
> The Linux client is non-compliant because it sends two chunks. A compliant server
ignores the
> second chunk, so this is functionally harmless (but a waste of resources).
> 
> The Linux server is non-compliant because it _requires_ the XDR pad chunk. A compliant
client
> (eg. Linux with pad optimization enabled) does not interoperate with it.
> 
> > And if I change the server
> > to only consume 1, then everything unaligned will break?
> 
> If you change the server to consume only the first chunk, but do not also make it deal
with XDR
> padding as recommended in chapter 3 of RFC 5666, then WRITEs with a length that is not a
> multiple of four will fail. SYMLINKs with a large payload will also have this problem.
> 

Thanks Chuck for clarifying this!  So I'm going to defer this issue and fix it with a
subsequent patch to only process 1 chunk and handle pad correctly.

Steve.


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[V2,RFC,2/3] svcrdma: Recvfrom changes

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