| Message ID | 6aa0c662a3fec17a1ade512e7bbb519aa49e6e4d.1660635140.git.asml.silence@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | io_uring zc notification tag override | expand |
Am 16.08.22 um 09:42 schrieb Pavel Begunkov: > Considering limited amount of slots some users struggle with > registration time notification tag assignment as it's hard to manage > notifications using sequence numbers. Add a simple feature that copies > sqe->user_data of a send(+flush) request into the notification CQE it > flushes (and only when it's flushes). > > Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> > --- > include/uapi/linux/io_uring.h | 4 ++++ > io_uring/net.c | 6 +++++- > 2 files changed, 9 insertions(+), 1 deletion(-) > > diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h > index 20368394870e..91e7944c9c78 100644 > --- a/include/uapi/linux/io_uring.h > +++ b/include/uapi/linux/io_uring.h > @@ -280,11 +280,15 @@ enum io_uring_op { > * > * IORING_RECVSEND_NOTIF_FLUSH Flush a notification after a successful > * successful. Only for zerocopy sends. > + * > + * IORING_RECVSEND_NOTIF_COPY_TAG Copy request's user_data into the notification > + * completion even if it's flushed. > */ > #define IORING_RECVSEND_POLL_FIRST (1U << 0) > #define IORING_RECV_MULTISHOT (1U << 1) > #define IORING_RECVSEND_FIXED_BUF (1U << 2) > #define IORING_RECVSEND_NOTIF_FLUSH (1U << 3) > +#define IORING_RECVSEND_NOTIF_COPY_TAG (1U << 4) > > /* cqe->res mask for extracting the notification sequence number */ > #define IORING_NOTIF_SEQ_MASK 0xFFFFU > diff --git a/io_uring/net.c b/io_uring/net.c > index bd3fad9536ef..4d271a269979 100644 > --- a/io_uring/net.c > +++ b/io_uring/net.c > @@ -858,7 +858,9 @@ int io_sendzc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe) > > zc->flags = READ_ONCE(sqe->ioprio); > if (zc->flags & ~(IORING_RECVSEND_POLL_FIRST | > - IORING_RECVSEND_FIXED_BUF | IORING_RECVSEND_NOTIF_FLUSH)) > + IORING_RECVSEND_FIXED_BUF | > + IORING_RECVSEND_NOTIF_FLUSH | > + IORING_RECVSEND_NOTIF_COPY_TAG)) > return -EINVAL; > if (zc->flags & IORING_RECVSEND_FIXED_BUF) { > unsigned idx = READ_ONCE(sqe->buf_index); > @@ -1024,6 +1026,8 @@ int io_sendzc(struct io_kiocb *req, unsigned int issue_flags) > if (ret == -ERESTARTSYS) > ret = -EINTR; > } else if (zc->flags & IORING_RECVSEND_NOTIF_FLUSH) { > + if (zc->flags & IORING_RECVSEND_NOTIF_COPY_TAG) > + notif->cqe.user_data = req->cqe.user_data; > io_notif_slot_flush_submit(notif_slot, 0); > } This would work but it seems to be confusing. Can't we have a slot-less mode, with slot_idx==U16_MAX, where we always allocate a new notif for each request, this would then get the same user_data and would be referenced on the request in order to reuse the same notif on an async retry after a short send. And this notif will always be flushed at the end of the request. This: struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx, struct io_notif_slot *slot) would change to: struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx, __u64 cqe_user_data, __s32 cqe_res) and: void io_notif_slot_flush(struct io_notif_slot *slot) __must_hold(&ctx->uring_lock) (__must_hold looks wrong there...) could just be: void io_notif_flush(struct io_notif_*notif) What do you think? It would remove the whole notif slot complexity from caller using IORING_RECVSEND_NOTIF_FLUSH for every request anyway. metze
On Tue, 2022-08-16 at 08:42 +0100, Pavel Begunkov wrote: > Considering limited amount of slots some users struggle with > registration time notification tag assignment as it's hard to manage > notifications using sequence numbers. Add a simple feature that > copies > sqe->user_data of a send(+flush) request into the notification CQE it > flushes (and only when it's flushes). I think for this to be useful I think it would also be needed to have flags on the generated CQE. If there are more CQEs coming for the same request it should have IORING_CQE_F_MORE set. Otherwise user space would not be able to know if it is able to reuse local data. Additionally it would need to provide a way of disambiguating the send CQE with the flush CQE. Dylan
On 8/16/22 09:37, Dylan Yudaken wrote: > On Tue, 2022-08-16 at 08:42 +0100, Pavel Begunkov wrote: >> Considering limited amount of slots some users struggle with >> registration time notification tag assignment as it's hard to manage >> notifications using sequence numbers. Add a simple feature that >> copies >> sqe->user_data of a send(+flush) request into the notification CQE it >> flushes (and only when it's flushes). > > I think for this to be useful I think it would also be needed to have > flags on the generated CQE. > > If there are more CQEs coming for the same request it should have > IORING_CQE_F_MORE set. Otherwise user space would not be able to know > if it is able to reuse local data. If you want to have: expect_more = cqe->flags & IORING_CQE_F_MORE; Then in the current form you can perfectly do that with // MSG_WAITALL expect_more = (cqe->res == io_len); // !MSG_WAITALL, expect_more = (cqe->res >= 0); But might be more convenient to have IORING_CQE_F_MORE set, one problem is a slight change of (implicit) semantics, i.e. we don't execute linked requests when filling a IORING_CQE_F_MORE CQE + CQE ordering implied from that. It's maybe worth to not rely on the link failing concept for deciding whether to flush or not. > Additionally it would need to provide a way of disambiguating the send > CQE with the flush CQE. Do you mean like IORING_CQE_F_NOTIF from 1/2?
On Wed, 2022-08-17 at 11:48 +0100, Pavel Begunkov wrote: > On 8/16/22 09:37, Dylan Yudaken wrote: > > On Tue, 2022-08-16 at 08:42 +0100, Pavel Begunkov wrote: > > > Considering limited amount of slots some users struggle with > > > registration time notification tag assignment as it's hard to > > > manage > > > notifications using sequence numbers. Add a simple feature that > > > copies > > > sqe->user_data of a send(+flush) request into the notification > > > CQE it > > > flushes (and only when it's flushes). > > > > I think for this to be useful I think it would also be needed to > > have > > flags on the generated CQE. > > > > If there are more CQEs coming for the same request it should have > > IORING_CQE_F_MORE set. Otherwise user space would not be able to > > know > > if it is able to reuse local data. > > If you want to have: > > expect_more = cqe->flags & IORING_CQE_F_MORE; > > Then in the current form you can perfectly do that with > > // MSG_WAITALL > expect_more = (cqe->res == io_len); > // !MSG_WAITALL, > expect_more = (cqe->res >= 0); > > But might be more convenient to have IORING_CQE_F_MORE set, > one problem is a slight change of (implicit) semantics, i.e. > we don't execute linked requests when filling a IORING_CQE_F_MORE > CQE + CQE ordering implied from that. > > It's maybe worth to not rely on the link failing concept for > deciding whether to flush or not. Is the ordering guaranteed then to be <send cqe>, <notif cqe>? If so I would put the IORING_CQE_F_MORE more as a nice to have for consistency with other ops > > > > Additionally it would need to provide a way of disambiguating the > > send > > CQE with the flush CQE. > > Do you mean like IORING_CQE_F_NOTIF from 1/2? > Apologies - I missed that
On 8/16/22 09:23, Stefan Metzmacher wrote: > Am 16.08.22 um 09:42 schrieb Pavel Begunkov: >> Considering limited amount of slots some users struggle with >> registration time notification tag assignment as it's hard to manage >> notifications using sequence numbers. Add a simple feature that copies >> sqe->user_data of a send(+flush) request into the notification CQE it >> flushes (and only when it's flushes). >> >> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> >> --- >> include/uapi/linux/io_uring.h | 4 ++++ >> io_uring/net.c | 6 +++++- >> 2 files changed, 9 insertions(+), 1 deletion(-) >> >> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h >> index 20368394870e..91e7944c9c78 100644 >> --- a/include/uapi/linux/io_uring.h >> +++ b/include/uapi/linux/io_uring.h >> @@ -280,11 +280,15 @@ enum io_uring_op { >> * >> * IORING_RECVSEND_NOTIF_FLUSH Flush a notification after a successful >> * successful. Only for zerocopy sends. >> + * >> + * IORING_RECVSEND_NOTIF_COPY_TAG Copy request's user_data into the notification >> + * completion even if it's flushed. >> */ >> #define IORING_RECVSEND_POLL_FIRST (1U << 0) >> #define IORING_RECV_MULTISHOT (1U << 1) >> #define IORING_RECVSEND_FIXED_BUF (1U << 2) >> #define IORING_RECVSEND_NOTIF_FLUSH (1U << 3) >> +#define IORING_RECVSEND_NOTIF_COPY_TAG (1U << 4) >> /* cqe->res mask for extracting the notification sequence number */ >> #define IORING_NOTIF_SEQ_MASK 0xFFFFU >> diff --git a/io_uring/net.c b/io_uring/net.c >> index bd3fad9536ef..4d271a269979 100644 >> --- a/io_uring/net.c >> +++ b/io_uring/net.c >> @@ -858,7 +858,9 @@ int io_sendzc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe) >> zc->flags = READ_ONCE(sqe->ioprio); >> if (zc->flags & ~(IORING_RECVSEND_POLL_FIRST | >> - IORING_RECVSEND_FIXED_BUF | IORING_RECVSEND_NOTIF_FLUSH)) >> + IORING_RECVSEND_FIXED_BUF | >> + IORING_RECVSEND_NOTIF_FLUSH | >> + IORING_RECVSEND_NOTIF_COPY_TAG)) >> return -EINVAL; >> if (zc->flags & IORING_RECVSEND_FIXED_BUF) { >> unsigned idx = READ_ONCE(sqe->buf_index); >> @@ -1024,6 +1026,8 @@ int io_sendzc(struct io_kiocb *req, unsigned int issue_flags) >> if (ret == -ERESTARTSYS) >> ret = -EINTR; >> } else if (zc->flags & IORING_RECVSEND_NOTIF_FLUSH) { >> + if (zc->flags & IORING_RECVSEND_NOTIF_COPY_TAG) >> + notif->cqe.user_data = req->cqe.user_data; >> io_notif_slot_flush_submit(notif_slot, 0); >> } > > This would work but it seems to be confusing. > > Can't we have a slot-less mode, with slot_idx==U16_MAX, > where we always allocate a new notif for each request, > this would then get the same user_data and would be referenced on the > request in order to reuse the same notif on an async retry after a short send. Ok, retries may make slots managing much harder, let me think > And this notif will always be flushed at the end of the request. > > This: > > struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx, > struct io_notif_slot *slot) > > would change to: > > struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx, > __u64 cqe_user_data, > __s32 cqe_res) > > > and: > > void io_notif_slot_flush(struct io_notif_slot *slot) __must_hold(&ctx->uring_lock) > > (__must_hold looks wrong there...) Nope, it should be there > could just be: > > void io_notif_flush(struct io_notif_*notif) > > What do you think? It would remove the whole notif slot complexity > from caller using IORING_RECVSEND_NOTIF_FLUSH for every request anyway. The downside is that requests then should be pretty large or it'll lose in performance. Surely not a problem for 8MB per request but even 4KB won't suffice. And users may want to put in smaller chunks on the wire instead of waiting for mode data to let tcp handle pacing and potentially improve latencies by sending earlier. On the other hand that one notification per request idea mentioned before can extended to 1-2 CQEs per request, which is interestingly the approach zc send discussions started with.
On 8/17/22 13:04, Dylan Yudaken wrote: > On Wed, 2022-08-17 at 11:48 +0100, Pavel Begunkov wrote: >> On 8/16/22 09:37, Dylan Yudaken wrote: >>> On Tue, 2022-08-16 at 08:42 +0100, Pavel Begunkov wrote: >>>> Considering limited amount of slots some users struggle with >>>> registration time notification tag assignment as it's hard to >>>> manage >>>> notifications using sequence numbers. Add a simple feature that >>>> copies >>>> sqe->user_data of a send(+flush) request into the notification >>>> CQE it >>>> flushes (and only when it's flushes). >>> >>> I think for this to be useful I think it would also be needed to >>> have >>> flags on the generated CQE. >>> >>> If there are more CQEs coming for the same request it should have >>> IORING_CQE_F_MORE set. Otherwise user space would not be able to >>> know >>> if it is able to reuse local data. >> >> If you want to have: >> >> expect_more = cqe->flags & IORING_CQE_F_MORE; >> >> Then in the current form you can perfectly do that with >> >> // MSG_WAITALL >> expect_more = (cqe->res == io_len); >> // !MSG_WAITALL, >> expect_more = (cqe->res >= 0); >> >> But might be more convenient to have IORING_CQE_F_MORE set, >> one problem is a slight change of (implicit) semantics, i.e. >> we don't execute linked requests when filling a IORING_CQE_F_MORE >> CQE + CQE ordering implied from that. >> >> It's maybe worth to not rely on the link failing concept for >> deciding whether to flush or not. > > Is the ordering guaranteed then to be <send cqe>, <notif cqe>? Not yet, need to send this patch https://github.com/isilence/linux/commit/9a1464905be3fc0cee4f68b01e43c5ad14a05b06 > If so I would put the IORING_CQE_F_MORE more as a nice to have for > consistency with other ops > >> >> >>> Additionally it would need to provide a way of disambiguating the >>> send >>> CQE with the flush CQE. >> >> Do you mean like IORING_CQE_F_NOTIF from 1/2? >> > > Apologies - I missed that >
Am 17.08.22 um 14:42 schrieb Pavel Begunkov: > On 8/16/22 09:23, Stefan Metzmacher wrote: >> Am 16.08.22 um 09:42 schrieb Pavel Begunkov: >>> Considering limited amount of slots some users struggle with >>> registration time notification tag assignment as it's hard to manage >>> notifications using sequence numbers. Add a simple feature that copies >>> sqe->user_data of a send(+flush) request into the notification CQE it >>> flushes (and only when it's flushes). >>> >>> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> >>> --- >>> include/uapi/linux/io_uring.h | 4 ++++ >>> io_uring/net.c | 6 +++++- >>> 2 files changed, 9 insertions(+), 1 deletion(-) >>> >>> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h >>> index 20368394870e..91e7944c9c78 100644 >>> --- a/include/uapi/linux/io_uring.h >>> +++ b/include/uapi/linux/io_uring.h >>> @@ -280,11 +280,15 @@ enum io_uring_op { >>> * >>> * IORING_RECVSEND_NOTIF_FLUSH Flush a notification after a successful >>> * successful. Only for zerocopy sends. >>> + * >>> + * IORING_RECVSEND_NOTIF_COPY_TAG Copy request's user_data into the notification >>> + * completion even if it's flushed. >>> */ >>> #define IORING_RECVSEND_POLL_FIRST (1U << 0) >>> #define IORING_RECV_MULTISHOT (1U << 1) >>> #define IORING_RECVSEND_FIXED_BUF (1U << 2) >>> #define IORING_RECVSEND_NOTIF_FLUSH (1U << 3) >>> +#define IORING_RECVSEND_NOTIF_COPY_TAG (1U << 4) >>> /* cqe->res mask for extracting the notification sequence number */ >>> #define IORING_NOTIF_SEQ_MASK 0xFFFFU >>> diff --git a/io_uring/net.c b/io_uring/net.c >>> index bd3fad9536ef..4d271a269979 100644 >>> --- a/io_uring/net.c >>> +++ b/io_uring/net.c >>> @@ -858,7 +858,9 @@ int io_sendzc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe) >>> zc->flags = READ_ONCE(sqe->ioprio); >>> if (zc->flags & ~(IORING_RECVSEND_POLL_FIRST | >>> - IORING_RECVSEND_FIXED_BUF | IORING_RECVSEND_NOTIF_FLUSH)) >>> + IORING_RECVSEND_FIXED_BUF | >>> + IORING_RECVSEND_NOTIF_FLUSH | >>> + IORING_RECVSEND_NOTIF_COPY_TAG)) >>> return -EINVAL; >>> if (zc->flags & IORING_RECVSEND_FIXED_BUF) { >>> unsigned idx = READ_ONCE(sqe->buf_index); >>> @@ -1024,6 +1026,8 @@ int io_sendzc(struct io_kiocb *req, unsigned int issue_flags) >>> if (ret == -ERESTARTSYS) >>> ret = -EINTR; >>> } else if (zc->flags & IORING_RECVSEND_NOTIF_FLUSH) { >>> + if (zc->flags & IORING_RECVSEND_NOTIF_COPY_TAG) >>> + notif->cqe.user_data = req->cqe.user_data; >>> io_notif_slot_flush_submit(notif_slot, 0); >>> } >> >> This would work but it seems to be confusing. >> >> Can't we have a slot-less mode, with slot_idx==U16_MAX, >> where we always allocate a new notif for each request, >> this would then get the same user_data and would be referenced on the >> request in order to reuse the same notif on an async retry after a short send. > > Ok, retries may make slots managing much harder, let me think With retries it would be much saner to use the same notif for the whole request. So keeping it referenced as zc->notif might be a way, maybe doing that in the _prep function in order to do it just once, then we don't need zc->slot_idx anymore. >> And this notif will always be flushed at the end of the request. >> >> This: >> >> struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx, >> struct io_notif_slot *slot) >> >> would change to: >> >> struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx, >> __u64 cqe_user_data, >> __s32 cqe_res) >> >> >> and: >> >> void io_notif_slot_flush(struct io_notif_slot *slot) __must_hold(&ctx->uring_lock) >> >> (__must_hold looks wrong there...) > > Nope, it should be there Shouldn't it be something like __must_hold(&slot->notif->ctx->uring_lock) There is not 'ctx' argument. >> could just be: >> >> void io_notif_flush(struct io_notif_*notif) >> >> What do you think? It would remove the whole notif slot complexity >> from caller using IORING_RECVSEND_NOTIF_FLUSH for every request anyway. > > The downside is that requests then should be pretty large or it'll > lose in performance. Surely not a problem for 8MB per request but > even 4KB won't suffice. And users may want to put in smaller chunks > on the wire instead of waiting for mode data to let tcp handle > pacing and potentially improve latencies by sending earlier. If this is optional applications can decide what fits better. > On the other hand that one notification per request idea mentioned > before can extended to 1-2 CQEs per request, which is interestingly > the approach zc send discussions started with. In order to make use of any of this I need any way to get 2 CQEs with user_data being the same or related. The only benefit for with slots is being able to avoid or batch additional CQEs, correct? Or is there more to it? metze
On 8/18/22 19:13, Stefan Metzmacher wrote: > Am 17.08.22 um 14:42 schrieb Pavel Begunkov: >> On 8/16/22 09:23, Stefan Metzmacher wrote: >>> Am 16.08.22 um 09:42 schrieb Pavel Begunkov: >>>> Considering limited amount of slots some users struggle with >>>> registration time notification tag assignment as it's hard to manage >>>> notifications using sequence numbers. Add a simple feature that copies >>>> sqe->user_data of a send(+flush) request into the notification CQE it >>>> flushes (and only when it's flushes). >>>> >>>> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> >>>> --- >>>> include/uapi/linux/io_uring.h | 4 ++++ >>>> io_uring/net.c | 6 +++++- >>>> 2 files changed, 9 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h >>>> index 20368394870e..91e7944c9c78 100644 >>>> --- a/include/uapi/linux/io_uring.h >>>> +++ b/include/uapi/linux/io_uring.h >>>> @@ -280,11 +280,15 @@ enum io_uring_op { >>>> * >>>> * IORING_RECVSEND_NOTIF_FLUSH Flush a notification after a successful >>>> * successful. Only for zerocopy sends. >>>> + * >>>> + * IORING_RECVSEND_NOTIF_COPY_TAG Copy request's user_data into the notification >>>> + * completion even if it's flushed. >>>> */ >>>> #define IORING_RECVSEND_POLL_FIRST (1U << 0) >>>> #define IORING_RECV_MULTISHOT (1U << 1) >>>> #define IORING_RECVSEND_FIXED_BUF (1U << 2) >>>> #define IORING_RECVSEND_NOTIF_FLUSH (1U << 3) >>>> +#define IORING_RECVSEND_NOTIF_COPY_TAG (1U << 4) >>>> /* cqe->res mask for extracting the notification sequence number */ >>>> #define IORING_NOTIF_SEQ_MASK 0xFFFFU >>>> diff --git a/io_uring/net.c b/io_uring/net.c >>>> index bd3fad9536ef..4d271a269979 100644 >>>> --- a/io_uring/net.c >>>> +++ b/io_uring/net.c >>>> @@ -858,7 +858,9 @@ int io_sendzc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe) >>>> zc->flags = READ_ONCE(sqe->ioprio); >>>> if (zc->flags & ~(IORING_RECVSEND_POLL_FIRST | >>>> - IORING_RECVSEND_FIXED_BUF | IORING_RECVSEND_NOTIF_FLUSH)) >>>> + IORING_RECVSEND_FIXED_BUF | >>>> + IORING_RECVSEND_NOTIF_FLUSH | >>>> + IORING_RECVSEND_NOTIF_COPY_TAG)) >>>> return -EINVAL; >>>> if (zc->flags & IORING_RECVSEND_FIXED_BUF) { >>>> unsigned idx = READ_ONCE(sqe->buf_index); >>>> @@ -1024,6 +1026,8 @@ int io_sendzc(struct io_kiocb *req, unsigned int issue_flags) >>>> if (ret == -ERESTARTSYS) >>>> ret = -EINTR; >>>> } else if (zc->flags & IORING_RECVSEND_NOTIF_FLUSH) { >>>> + if (zc->flags & IORING_RECVSEND_NOTIF_COPY_TAG) >>>> + notif->cqe.user_data = req->cqe.user_data; >>>> io_notif_slot_flush_submit(notif_slot, 0); >>>> } >>> >>> This would work but it seems to be confusing. >>> >>> Can't we have a slot-less mode, with slot_idx==U16_MAX, >>> where we always allocate a new notif for each request, >>> this would then get the same user_data and would be referenced on the >>> request in order to reuse the same notif on an async retry after a short send. >> >> Ok, retries may make slots managing much harder, let me think > > With retries it would be much saner to use the same > notif for the whole request. So keeping it referenced > as zc->notif might be a way, maybe doing that in the _prep > function in order to do it just once, then we don't need > zc->slot_idx anymore. Even though it's possible atm with some userspace consideration, it's definitely should be patched up. >>> And this notif will always be flushed at the end of the request. >>> >>> This: >>> >>> struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx, >>> struct io_notif_slot *slot) >>> >>> would change to: >>> >>> struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx, >>> __u64 cqe_user_data, >>> __s32 cqe_res) >>> >>> >>> and: >>> >>> void io_notif_slot_flush(struct io_notif_slot *slot) __must_hold(&ctx->uring_lock) >>> >>> (__must_hold looks wrong there...) >> >> Nope, it should be there > > Shouldn't it be something like > __must_hold(&slot->notif->ctx->uring_lock) > > There is not 'ctx' argument. Ah, in this sense, agree >>> What do you think? It would remove the whole notif slot complexity >>> from caller using IORING_RECVSEND_NOTIF_FLUSH for every request anyway. >> >> The downside is that requests then should be pretty large or it'll >> lose in performance. Surely not a problem for 8MB per request but >> even 4KB won't suffice. And users may want to put in smaller chunks >> on the wire instead of waiting for mode data to let tcp handle >> pacing and potentially improve latencies by sending earlier. > > If this is optional applications can decide what fits better. > >> On the other hand that one notification per request idea mentioned >> before can extended to 1-2 CQEs per request, which is interestingly >> the approach zc send discussions started with. > > In order to make use of any of this I need any way > to get 2 CQEs with user_data being the same or related. The idea described above will post 2 CQEs (mostly) per request as you want with an optional way to have only 1 CQE. My current sentiment is to kill all the slot business, leave this 1-2 CQE per request and see if there are users for whom it won't be enough. It's anyway just a slight deviation from what I wanted to push as a complimentary interface. > The only benefit for with slots is being able to avoid or > batch additional CQEs, correct? Or is there more to it? CQE batching is a lesser problem, I'm more concerned of how it sticks with the network. In short, it'll hugely underperform with TCP if requests are not large enough. A simple bench with some hacks, localhost, TCP, run by ./msg_zerocopy -6 -r tcp -s <size> & ./io_uring_zerocopy_tx -6 -D "::1" -s <size> -m <0,2> tcp non-zerocopy: 4000B: tx=8711880 (MB=33233), tx/s=1742376 (MB/s=6646) 16000B: tx=3196528 (MB=48775), tx/s=639305 (MB/s=9755) 60000B: tx=1036536 (MB=59311), tx/s=207307 (MB/s=11862) zerocopy: 4000B: tx=3003488 (MB=11457), tx/s=600697 (MB/s=2291) 16000B: tx=2940296 (MB=44865), tx/s=588059 (MB/s=8973) 60000B: tx=2621792 (MB=150020), tx/s=524358 (MB/s=30004) Reusing notifications with slots will change the picture. And it this has nothing to do with io_uring overhead like CQE posting and so on.
Am 19.08.22 um 13:42 schrieb Pavel Begunkov: > On 8/18/22 19:13, Stefan Metzmacher wrote: >> Am 17.08.22 um 14:42 schrieb Pavel Begunkov: >>> On 8/16/22 09:23, Stefan Metzmacher wrote: >>>> Am 16.08.22 um 09:42 schrieb Pavel Begunkov: >>>>> Considering limited amount of slots some users struggle with >>>>> registration time notification tag assignment as it's hard to manage >>>>> notifications using sequence numbers. Add a simple feature that copies >>>>> sqe->user_data of a send(+flush) request into the notification CQE it >>>>> flushes (and only when it's flushes). >>>>> >>>>> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> >>>>> --- >>>>> include/uapi/linux/io_uring.h | 4 ++++ >>>>> io_uring/net.c | 6 +++++- >>>>> 2 files changed, 9 insertions(+), 1 deletion(-) >>>>> >>>>> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h >>>>> index 20368394870e..91e7944c9c78 100644 >>>>> --- a/include/uapi/linux/io_uring.h >>>>> +++ b/include/uapi/linux/io_uring.h >>>>> @@ -280,11 +280,15 @@ enum io_uring_op { >>>>> * >>>>> * IORING_RECVSEND_NOTIF_FLUSH Flush a notification after a successful >>>>> * successful. Only for zerocopy sends. >>>>> + * >>>>> + * IORING_RECVSEND_NOTIF_COPY_TAG Copy request's user_data into the notification >>>>> + * completion even if it's flushed. >>>>> */ >>>>> #define IORING_RECVSEND_POLL_FIRST (1U << 0) >>>>> #define IORING_RECV_MULTISHOT (1U << 1) >>>>> #define IORING_RECVSEND_FIXED_BUF (1U << 2) >>>>> #define IORING_RECVSEND_NOTIF_FLUSH (1U << 3) >>>>> +#define IORING_RECVSEND_NOTIF_COPY_TAG (1U << 4) >>>>> /* cqe->res mask for extracting the notification sequence number */ >>>>> #define IORING_NOTIF_SEQ_MASK 0xFFFFU >>>>> diff --git a/io_uring/net.c b/io_uring/net.c >>>>> index bd3fad9536ef..4d271a269979 100644 >>>>> --- a/io_uring/net.c >>>>> +++ b/io_uring/net.c >>>>> @@ -858,7 +858,9 @@ int io_sendzc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe) >>>>> zc->flags = READ_ONCE(sqe->ioprio); >>>>> if (zc->flags & ~(IORING_RECVSEND_POLL_FIRST | >>>>> - IORING_RECVSEND_FIXED_BUF | IORING_RECVSEND_NOTIF_FLUSH)) >>>>> + IORING_RECVSEND_FIXED_BUF | >>>>> + IORING_RECVSEND_NOTIF_FLUSH | >>>>> + IORING_RECVSEND_NOTIF_COPY_TAG)) >>>>> return -EINVAL; >>>>> if (zc->flags & IORING_RECVSEND_FIXED_BUF) { >>>>> unsigned idx = READ_ONCE(sqe->buf_index); >>>>> @@ -1024,6 +1026,8 @@ int io_sendzc(struct io_kiocb *req, unsigned int issue_flags) >>>>> if (ret == -ERESTARTSYS) >>>>> ret = -EINTR; >>>>> } else if (zc->flags & IORING_RECVSEND_NOTIF_FLUSH) { >>>>> + if (zc->flags & IORING_RECVSEND_NOTIF_COPY_TAG) >>>>> + notif->cqe.user_data = req->cqe.user_data; >>>>> io_notif_slot_flush_submit(notif_slot, 0); >>>>> } >>>> >>>> This would work but it seems to be confusing. >>>> >>>> Can't we have a slot-less mode, with slot_idx==U16_MAX, >>>> where we always allocate a new notif for each request, >>>> this would then get the same user_data and would be referenced on the >>>> request in order to reuse the same notif on an async retry after a short send. >>> >>> Ok, retries may make slots managing much harder, let me think >> >> With retries it would be much saner to use the same >> notif for the whole request. So keeping it referenced >> as zc->notif might be a way, maybe doing that in the _prep >> function in order to do it just once, then we don't need >> zc->slot_idx anymore. > > Even though it's possible atm with some userspace consideration, > it's definitely should be patched up. > >>>> And this notif will always be flushed at the end of the request. >>>> >>>> This: >>>> >>>> struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx, >>>> struct io_notif_slot *slot) >>>> >>>> would change to: >>>> >>>> struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx, >>>> __u64 cqe_user_data, >>>> __s32 cqe_res) >>>> >>>> >>>> and: >>>> >>>> void io_notif_slot_flush(struct io_notif_slot *slot) __must_hold(&ctx->uring_lock) >>>> >>>> (__must_hold looks wrong there...) >>> >>> Nope, it should be there >> >> Shouldn't it be something like >> __must_hold(&slot->notif->ctx->uring_lock) >> >> There is not 'ctx' argument. > > Ah, in this sense, agree > >>>> What do you think? It would remove the whole notif slot complexity >>>> from caller using IORING_RECVSEND_NOTIF_FLUSH for every request anyway. >>> >>> The downside is that requests then should be pretty large or it'll >>> lose in performance. Surely not a problem for 8MB per request but >>> even 4KB won't suffice. And users may want to put in smaller chunks >>> on the wire instead of waiting for mode data to let tcp handle >>> pacing and potentially improve latencies by sending earlier. >> >> If this is optional applications can decide what fits better. >> >>> On the other hand that one notification per request idea mentioned >>> before can extended to 1-2 CQEs per request, which is interestingly >>> the approach zc send discussions started with. >> >> In order to make use of any of this I need any way >> to get 2 CQEs with user_data being the same or related. > > The idea described above will post 2 CQEs (mostly) per request > as you want with an optional way to have only 1 CQE. My current > sentiment is to kill all the slot business, leave this 1-2 CQE > per request and see if there are users for whom it won't be > enough. It's anyway just a slight deviation from what I wanted > to push as a complimentary interface. Ah, ok, removing the slot stuff again would be fine for me... >> The only benefit for with slots is being able to avoid or >> batch additional CQEs, correct? Or is there more to it? > > CQE batching is a lesser problem, I'm more concerned of how > it sticks with the network. In short, it'll hugely underperform > with TCP if requests are not large enough. > > A simple bench with some hacks, localhost, TCP, run by > > ./msg_zerocopy -6 -r tcp -s <size> & > ./io_uring_zerocopy_tx -6 -D "::1" -s <size> -m <0,2> tcp > > > non-zerocopy: > 4000B: tx=8711880 (MB=33233), tx/s=1742376 (MB/s=6646) > 16000B: tx=3196528 (MB=48775), tx/s=639305 (MB/s=9755) > 60000B: tx=1036536 (MB=59311), tx/s=207307 (MB/s=11862) > > zerocopy: > 4000B: tx=3003488 (MB=11457), tx/s=600697 (MB/s=2291) > 16000B: tx=2940296 (MB=44865), tx/s=588059 (MB/s=8973) > 60000B: tx=2621792 (MB=150020), tx/s=524358 (MB/s=30004) So with something between 16k and 60k we reach the point where ZC starts to be faster, correct? Did you remove the loopback restriction as described in Documentation/networking/msg_zerocopy.rst ? Are the results similar when using ./msg_zerocopy -6 tcp -s <size> as client? And the reason is some page pinning overhead from iov_iter_get_pages2() in __zerocopy_sg_from_iter()? > Reusing notifications with slots will change the picture. > And it this has nothing to do with io_uring overhead like > CQE posting and so on. Hmm I don't understand how the number of notif structures would have any impact? Is it related to io_sg_from_iter()? metze
On 8/19/22 13:36, Stefan Metzmacher wrote: [...] >>>>> What do you think? It would remove the whole notif slot complexity >>>>> from caller using IORING_RECVSEND_NOTIF_FLUSH for every request anyway. >>>> >>>> The downside is that requests then should be pretty large or it'll >>>> lose in performance. Surely not a problem for 8MB per request but >>>> even 4KB won't suffice. And users may want to put in smaller chunks >>>> on the wire instead of waiting for mode data to let tcp handle >>>> pacing and potentially improve latencies by sending earlier. >>> >>> If this is optional applications can decide what fits better. >>> >>>> On the other hand that one notification per request idea mentioned >>>> before can extended to 1-2 CQEs per request, which is interestingly >>>> the approach zc send discussions started with. >>> >>> In order to make use of any of this I need any way >>> to get 2 CQEs with user_data being the same or related. >> >> The idea described above will post 2 CQEs (mostly) per request >> as you want with an optional way to have only 1 CQE. My current >> sentiment is to kill all the slot business, leave this 1-2 CQE >> per request and see if there are users for whom it won't be >> enough. It's anyway just a slight deviation from what I wanted >> to push as a complimentary interface. > > Ah, ok, removing the slot stuff again would be fine for me... > >>> The only benefit for with slots is being able to avoid or >>> batch additional CQEs, correct? Or is there more to it? >> >> CQE batching is a lesser problem, I'm more concerned of how >> it sticks with the network. In short, it'll hugely underperform >> with TCP if requests are not large enough. >> >> A simple bench with some hacks, localhost, TCP, run by >> >> ./msg_zerocopy -6 -r tcp -s <size> & >> ./io_uring_zerocopy_tx -6 -D "::1" -s <size> -m <0,2> tcp >> >> >> non-zerocopy: >> 4000B: tx=8711880 (MB=33233), tx/s=1742376 (MB/s=6646) >> 16000B: tx=3196528 (MB=48775), tx/s=639305 (MB/s=9755) >> 60000B: tx=1036536 (MB=59311), tx/s=207307 (MB/s=11862) >> >> zerocopy: >> 4000B: tx=3003488 (MB=11457), tx/s=600697 (MB/s=2291) >> 16000B: tx=2940296 (MB=44865), tx/s=588059 (MB/s=8973) >> 60000B: tx=2621792 (MB=150020), tx/s=524358 (MB/s=30004) > > So with something between 16k and 60k we reach the point where > ZC starts to be faster, correct? For this setup -- yes, should be somewhat around 16-20K, don't remember numbers for real hw, but I saw similar tendencies. > Did you remove the loopback restriction as described in > Documentation/networking/msg_zerocopy.rst ? right, it wouldn't outperform even with large payload otherwise > Are the results similar when using ./msg_zerocopy -6 tcp -s <size> > as client? Shouldn't be, it also batches multiple requests to a single (internal) notification and also exposes it to the userspace differently. > And the reason is some page pinning overhead from iov_iter_get_pages2() > in __zerocopy_sg_from_iter()? No, I was using registered buffers here, so instead of iov_iter_get_pages2() business zerocopy was doing io_uring/net.c:io_sg_from_iter(). And in any case overhead on pinning wouldn't drastically change it. >> Reusing notifications with slots will change the picture. >> And it this has nothing to do with io_uring overhead like >> CQE posting and so on. > > Hmm I don't understand how the number of notif structures > would have any impact? Is it related to io_sg_from_iter()? It comes from TCP stack force changing an skbuff every time it meets a new ubuf_info (i.e. a notification handle for simplicity), there is a slight bump on skb allocation overhead but the main problem is seemingly comes from tcp_push and so, feeding it down the stack. I don't think there is any fundamental reason for why it should be working so much slower but might be problematic from engineering perspective. I'll ask a bit around or maybe look myself if find time for that.
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h index 20368394870e..91e7944c9c78 100644 --- a/include/uapi/linux/io_uring.h +++ b/include/uapi/linux/io_uring.h @@ -280,11 +280,15 @@ enum io_uring_op { * * IORING_RECVSEND_NOTIF_FLUSH Flush a notification after a successful * successful. Only for zerocopy sends. + * + * IORING_RECVSEND_NOTIF_COPY_TAG Copy request's user_data into the notification + * completion even if it's flushed. */ #define IORING_RECVSEND_POLL_FIRST (1U << 0) #define IORING_RECV_MULTISHOT (1U << 1) #define IORING_RECVSEND_FIXED_BUF (1U << 2) #define IORING_RECVSEND_NOTIF_FLUSH (1U << 3) +#define IORING_RECVSEND_NOTIF_COPY_TAG (1U << 4) /* cqe->res mask for extracting the notification sequence number */ #define IORING_NOTIF_SEQ_MASK 0xFFFFU diff --git a/io_uring/net.c b/io_uring/net.c index bd3fad9536ef..4d271a269979 100644 --- a/io_uring/net.c +++ b/io_uring/net.c @@ -858,7 +858,9 @@ int io_sendzc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe) zc->flags = READ_ONCE(sqe->ioprio); if (zc->flags & ~(IORING_RECVSEND_POLL_FIRST | - IORING_RECVSEND_FIXED_BUF | IORING_RECVSEND_NOTIF_FLUSH)) + IORING_RECVSEND_FIXED_BUF | + IORING_RECVSEND_NOTIF_FLUSH | + IORING_RECVSEND_NOTIF_COPY_TAG)) return -EINVAL; if (zc->flags & IORING_RECVSEND_FIXED_BUF) { unsigned idx = READ_ONCE(sqe->buf_index); @@ -1024,6 +1026,8 @@ int io_sendzc(struct io_kiocb *req, unsigned int issue_flags) if (ret == -ERESTARTSYS) ret = -EINTR; } else if (zc->flags & IORING_RECVSEND_NOTIF_FLUSH) { + if (zc->flags & IORING_RECVSEND_NOTIF_COPY_TAG) + notif->cqe.user_data = req->cqe.user_data; io_notif_slot_flush_submit(notif_slot, 0); }
Considering limited amount of slots some users struggle with registration time notification tag assignment as it's hard to manage notifications using sequence numbers. Add a simple feature that copies sqe->user_data of a send(+flush) request into the notification CQE it flushes (and only when it's flushes). Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> --- include/uapi/linux/io_uring.h | 4 ++++ io_uring/net.c | 6 +++++- 2 files changed, 9 insertions(+), 1 deletion(-)