From patchwork Mon Dec 11 15:24:53 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Chuck Lever X-Patchwork-Id: 13487411 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 685BD3B184; Mon, 11 Dec 2023 15:24:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="LMVQ+r4P" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A4BFCC433C7; Mon, 11 Dec 2023 15:24:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1702308294; bh=jdchVgDmsZtECwiFg6aF5OPF0Qz+GiqmuHEdpGSnXtE=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=LMVQ+r4PcRjJfACop+BPqRzcPR4AiDY7LSQeZNUzqHVZs0sFie/08jBpstRqYFJPz rWYLIByCaMe6gUKdjkjkmBW4mFUngugfrVMf+ckcTcyzzojtikcVcFgWSYew4tZQd7 LbK9zq/fMoXi8vvC89qQ93w5IyQ9vK4VXmgec9Td8FBU5EDdtjdZ+fNt5rbFtQpWn9 LTWLH+xqQSC5+2WgJJzH8pDvGvS8ve+gNTVb0mk/K0yz2KL5IuRlbIJ3ER6Pk8Lk6C y92m3icsxa3m57RHuELpCvRiRfriTdE7n67i/zg8O9Z/qPcl9rfYtyqvDbmRtRwSvM sfOiDgNGKSuew== Subject: [PATCH v1 8/8] svcrdma: Increase the per-transport rw_ctx count From: Chuck Lever To: linux-nfs@vger.kernel.org, linux-rdma@vger.kernel.org Cc: tom@talpey.com Date: Mon, 11 Dec 2023 10:24:53 -0500 Message-ID: <170230829373.90242.11114271955743181616.stgit@bazille.1015granger.net> In-Reply-To: <170230788373.90242.9421368360904462120.stgit@bazille.1015granger.net> References: <170230788373.90242.9421368360904462120.stgit@bazille.1015granger.net> User-Agent: StGit/1.5 Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: Chuck Lever rdma_rw_mr_factor() returns the smallest number of MRs needed to move a particular number of pages. svcrdma currently asks for the number of MRs needed to move RPCSVC_MAXPAGES (a little over one megabyte), as that is the number of pages in the largest r/wsize the server supports. This call assumes that the client's NIC can bundle a full one megabyte payload in a single rdma_segment. In fact, most NICs cannot handle a full megabyte with a single rkey / rdma_segment. Clients will typically split even a single Read chunk into many segments. The server needs one MR to read each rdma_segment in a Read chunk, and thus each one needs an rw_ctx. svcrdma has been vastly underestimating the number of rw_ctxs needed to handle 64 RPC requests with large Read chunks using small rdma_segments. Unfortunately there doesn't seem to be a good way to estimate this number without knowing the client NIC's capabilities. Even then, the client RPC/RDMA implementation is still free to split a chunk into smaller segments (for example, it might be using physical registration, which needs an rdma_segment per page). The best we can do for now is choose a number that will guarantee forward progress in the worst case (one page per segment). At some later point, we could add some mechanisms to make this much less of a problem: - Add a core API to add more rw_ctxs to an already-established QP - svcrdma could treat rw_ctx exhaustion as a temporary error and try again - Limit the number of Reads in flight Signed-off-by: Chuck Lever --- net/sunrpc/xprtrdma/svc_rdma_transport.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c index 790841864153..0ceb2817ca4d 100644 --- a/net/sunrpc/xprtrdma/svc_rdma_transport.c +++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c @@ -422,8 +422,12 @@ static struct svc_xprt *svc_rdma_accept(struct svc_xprt *xprt) newxprt->sc_max_bc_requests = 2; } - ctxts = rdma_rw_mr_factor(dev, newxprt->sc_port_num, RPCSVC_MAXPAGES); - ctxts *= newxprt->sc_max_requests; + /* Arbitrarily estimate the number of rw_ctxs needed for + * this transport. This is enough rw_ctxs to make forward + * progress even if the client is using one rkey per page + * in each Read chunk. + */ + ctxts = 3 * RPCSVC_MAXPAGES; sq_depth = newxprt->sc_max_requests + newxprt->sc_max_bc_requests + 1; if (sq_depth > dev->attrs.max_qp_wr)