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Date: Thu, 20 Oct 2022 14:46:02 +0100
From: Pavel Begunkov <asml.silence@...il.com>
To: Stefan Metzmacher <metze@...ba.org>,
io-uring <io-uring@...r.kernel.org>, Jens Axboe <axboe@...nel.dk>
Cc: Jakub Kicinski <kuba@...nel.org>, netdev <netdev@...r.kernel.org>,
Dylan Yudaken <dylany@...com>
Subject: Re: IORING_SEND_NOTIF_REPORT_USAGE (was Re: IORING_CQE_F_COPIED)
On 10/20/22 11:04, Stefan Metzmacher wrote:
> Hi Pavel,
[...]
>
> So far I came up with a IORING_SEND_NOTIF_REPORT_USAGE opt-in flag
> and the reporting is done in cqe.res with IORING_NOTIF_USAGE_ZC_USED (0x00000001)
> and/or IORING_NOTIF_USAGE_ZC_COPIED (0x8000000). So the caller is also
> able to notice that some parts were able to use zero copy, while other
> fragments were copied.
Are we really interested in multihoming and probably some very edge cases?
I'd argue we're not and it should be a single bool hint indicating whether
zc is viable or not. It can do more complex calculations _if_ needed, e.g.
looking inside skb's and figure out how many bytes were copied but as for me
it should better be turned into a single bool in the end. Could also be the
number of bytes copied, but I don't think we can't have the accuracy for
that (e.g. what we're going to return if some protocol duplicates an skb
and sends to 2 different devices or is processing it in a pipeline?)
So the question is what is the use case for having 2 flags?
btw, now we've got another example why the report flag is a good idea,
we can't use cqe.res unconditionally because we want to have a "one CQE
per request" mode, but it's fine if we make it and the report flag
mutually exclusive.
> I haven't tested it yet, but I want to post it early...
>
> What do you think?
Keeping in mind potential backporting let's make it as simple and
short as possible first and then do optimisations on top.
> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> index ab7458033ee3..751fc4eff8d1 100644
> --- a/include/uapi/linux/io_uring.h
> +++ b/include/uapi/linux/io_uring.h
> @@ -296,10 +296,28 @@ enum io_uring_op {
> *
> * IORING_RECVSEND_FIXED_BUF Use registered buffers, the index is stored in
> * the buf_index field.
> + *
> + * IORING_SEND_NOTIF_REPORT_USAGE
> + * If SEND[MSG]_ZC should report
> + * the zerocopy usage in cqe.res
> + * for the IORING_CQE_F_NOTIF cqe.
> + * IORING_NOTIF_USAGE_ZC_USED if zero copy was used
> + * (at least partially).
> + * IORING_NOTIF_USAGE_ZC_COPIED if data was copied
> + * (at least partially).
> */
> #define IORING_RECVSEND_POLL_FIRST (1U << 0)
> #define IORING_RECV_MULTISHOT (1U << 1)
> #define IORING_RECVSEND_FIXED_BUF (1U << 2)
> +#define IORING_SEND_NOTIF_REPORT_USAGE (1U << 3)
> +
> +/*
> + * cqe.res for IORING_CQE_F_NOTIF if
> + * IORING_SEND_NOTIF_REPORT_USAGE was requested
> + */
> +#define IORING_NOTIF_USAGE_ZC_USED (1U << 0)
> +#define IORING_NOTIF_USAGE_ZC_COPIED (1U << 31)
> +
>
> /*
> * accept flags stored in sqe->ioprio
> diff --git a/io_uring/net.c b/io_uring/net.c
> index 735eec545115..a79d7d349e19 100644
> --- a/io_uring/net.c
> +++ b/io_uring/net.c
> @@ -946,9 +946,11 @@ int io_send_zc_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_FIXED_BUF |
> + IORING_SEND_NOTIF_REPORT_USAGE))
> return -EINVAL;
> - notif = zc->notif = io_alloc_notif(ctx);
> + notif = zc->notif = io_alloc_notif(ctx,
> + zc->flags & IORING_SEND_NOTIF_REPORT_USAGE);
> if (!notif)
> return -ENOMEM;
> notif->cqe.user_data = req->cqe.user_data;
> diff --git a/io_uring/notif.c b/io_uring/notif.c
> index e37c6569d82e..3844e3c8ad7e 100644
> --- a/io_uring/notif.c
> +++ b/io_uring/notif.c
> @@ -3,13 +3,14 @@
> #include <linux/file.h>
> #include <linux/slab.h>
> #include <linux/net.h>
> +#include <linux/errqueue.h>
Is it needed?
> #include <linux/io_uring.h>
>
> #include "io_uring.h"
> #include "notif.h"
> #include "rsrc.h"
>
> -static void __io_notif_complete_tw(struct io_kiocb *notif, bool *locked)
> +static inline void __io_notif_complete_tw(struct io_kiocb *notif, bool *locked)
Let's remove this hunk with inlining and do it later
> {
> struct io_notif_data *nd = io_notif_to_data(notif);
> struct io_ring_ctx *ctx = notif->ctx;
> @@ -21,20 +22,46 @@ static void __io_notif_complete_tw(struct io_kiocb *notif, bool *locked)
> io_req_task_complete(notif, locked);
> }
>
> -static void io_uring_tx_zerocopy_callback(struct sk_buff *skb,
> - struct ubuf_info *uarg,
> - bool success)
> +static inline void io_uring_tx_zerocopy_callback(struct sk_buff *skb,
> + struct ubuf_info *uarg,
> + bool success)
This one as well.
> {
> struct io_notif_data *nd = container_of(uarg, struct io_notif_data, uarg);
> struct io_kiocb *notif = cmd_to_io_kiocb(nd);
>
> if (refcount_dec_and_test(&uarg->refcnt)) {
> - notif->io_task_work.func = __io_notif_complete_tw;
> io_req_task_work_add(notif);
> }
> }
>
> -struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx)
> +static void __io_notif_complete_tw_report_usage(struct io_kiocb *notif, bool *locked)
Just shove all that into __io_notif_complete_tw().
> +{
> + struct io_notif_data *nd = io_notif_to_data(notif);
> +
> + if (likely(nd->zc_used))
> + notif->cqe.res |= IORING_NOTIF_USAGE_ZC_USED;
> +
> + if (unlikely(nd->zc_copied))
> + notif->cqe.res |= IORING_NOTIF_USAGE_ZC_COPIED;
> +
> + __io_notif_complete_tw(notif, locked);
> +}
> +
> +static void io_uring_tx_zerocopy_callback_report_usage(struct sk_buff *skb,
> + struct ubuf_info *uarg,
> + bool success)
> +{
> + struct io_notif_data *nd = container_of(uarg, struct io_notif_data, uarg);
> +
> + if (success && !nd->zc_used && skb)
> + nd->zc_used = true;
> + else if (unlikely(!success && !nd->zc_copied))
> + nd->zc_copied = true;
It's fine but racy, so let's WRITE_ONCE() to indicate it.
> +
> + io_uring_tx_zerocopy_callback(skb, uarg, success);
> +}
> +
> +struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx, bool report_usage)
> __must_hold(&ctx->uring_lock)
And it's better to kill this argument and init zc_used/copied
unconditionally.
> {
> struct io_kiocb *notif;
> @@ -54,7 +81,14 @@ struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx)
> nd = io_notif_to_data(notif);
> nd->account_pages = 0;
> nd->uarg.flags = SKBFL_ZEROCOPY_FRAG | SKBFL_DONT_ORPHAN;
> - nd->uarg.callback = io_uring_tx_zerocopy_callback;
> + if (report_usage) {
> + nd->zc_used = nd->zc_copied = false;
> + nd->uarg.callback = io_uring_tx_zerocopy_callback_report_usage;
> + notif->io_task_work.func = __io_notif_complete_tw_report_usage;
> + } else {
> + nd->uarg.callback = io_uring_tx_zerocopy_callback;
> + notif->io_task_work.func = __io_notif_complete_tw;
> + }
> refcount_set(&nd->uarg.refcnt, 1);
> return notif;
> }
> @@ -66,7 +100,6 @@ void io_notif_flush(struct io_kiocb *notif)
>
> /* drop slot's master ref */
> if (refcount_dec_and_test(&nd->uarg.refcnt)) {
> - notif->io_task_work.func = __io_notif_complete_tw;
> io_req_task_work_add(notif);
> }
> }
> diff --git a/io_uring/notif.h b/io_uring/notif.h
> index 5b4d710c8ca5..5ac7a2745e52 100644
> --- a/io_uring/notif.h
> +++ b/io_uring/notif.h
> @@ -13,10 +13,12 @@ struct io_notif_data {
> struct file *file;
> struct ubuf_info uarg;
> unsigned long account_pages;
> + bool zc_used;
> + bool zc_copied;
IIRC io_notif_data is fully packed in 6.1, so placing zc_{used,copied}
there might complicate backporting (if any). We can place them in io_kiocb
directly and move in 6.2. Alternatively account_pages doesn't have to be
long.
> };
>
> void io_notif_flush(struct io_kiocb *notif);
> -struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx);
> +struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx, bool report_usage);
>
> static inline struct io_notif_data *io_notif_to_data(struct io_kiocb *notif)
> {
>
--
Pavel Begunkov
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