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Message-ID: <273f154a-4cbd-2412-d056-a31fab5368d3@gmail.com>
Date: Fri, 21 Oct 2022 12:09:09 +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 10/21/22 10:36, Stefan Metzmacher wrote:
> Hi Pavel,
[...]
>> Right, I'm just tired of back porting patches by hand :)
>
> ok, I just assumed it would be 6.1 only.
I'm fine with 6.1 only, it'd make things easier. I thought from
your first postings you wanted it 6.0. Then we don't need to care
about the placing of the copied/used flags.
>>> Otherwise we could have IORING_CQE_F_COPIED by default without opt-in
>>> flag...
>
> Do you still want an opt-in flag to get IORING_CQE_F_COPIED?
> If so what name do you want it to be?
Ala a IORING_SEND_* flag? Yes please.
*_REPORT_USAGE was fine but I'd make it IORING_SEND_ZC_REPORT_USAGE.
And can be extended if there is more info needed in the future.
And I don't mind using a bit in cqe->res, makes cflags less polluted.
>>>>> +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.
>>>
>>> I don't see how this could be a problem, but I can add it.
>>
>> It's not a problem, but better to be a little be more explicit
>> about parallel writes.
>
> ok.
>
>>>>> 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.
>>>
>>> As far as I can see kernel-dk-block/io_uring-6.1 alread has your
>>> shrink patches included...
>>
>> Sorry, I mean 6.0
>
> So you want to backport to 6.0?
>
> Find the current version below, sizeof(struct io_kiocb) will grow from
> 3*64 + 24 to 3*64 + 32 (on x64_64) to it stays within 4 cache lines.
>
> I tried this first:
>
> union {
> u8 iopoll_completed;
> struct {
> u8 zc_used:1;
> u8 zc_copied:1;
> };
> };
>
> But then WRITE_ONCE() complains about a bitfield write.
rightfully so, it can't be a bitfield as it would be racy
and not only in theory this time.
> So let me now about the opt-in flag and I'll prepare real commits
> including a patch that moves from struct io_kiocb to struct io_notif_data
> on top.
Yeah, better to be opt-in, but apart from it and comments above
looks good.
> diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
> index f5b687a787a3..189152ad78d6 100644
> --- a/include/linux/io_uring_types.h
> +++ b/include/linux/io_uring_types.h
> @@ -515,6 +515,9 @@ struct io_kiocb {
> u8 opcode;
> /* polled IO has completed */
> u8 iopoll_completed;
> + /* these will be moved to struct io_notif_data in 6.1 */
> + bool zc_used;
> + bool zc_copied;
> /*
> * Can be either a fixed buffer index, or used with provided buffers.
> * For the latter, before issue it points to the buffer group ID,
> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> index ab7458033ee3..738d6234d1d9 100644
> --- a/include/uapi/linux/io_uring.h
> +++ b/include/uapi/linux/io_uring.h
> @@ -350,6 +350,7 @@ struct io_uring_cqe {
> #define IORING_CQE_F_MORE (1U << 1)
> #define IORING_CQE_F_SOCK_NONEMPTY (1U << 2)
> #define IORING_CQE_F_NOTIF (1U << 3)
> +#define IORING_CQE_F_COPIED (1U << 4)
>
> enum {
> IORING_CQE_BUFFER_SHIFT = 16,
> diff --git a/io_uring/notif.c b/io_uring/notif.c
> index e37c6569d82e..033aca064b10 100644
> --- a/io_uring/notif.c
> +++ b/io_uring/notif.c
> @@ -18,6 +18,10 @@ static void __io_notif_complete_tw(struct io_kiocb *notif, bool *locked)
> __io_unaccount_mem(ctx->user, nd->account_pages);
> nd->account_pages = 0;
> }
> +
> + if (notif->zc_copied || !notif->zc_used)
> + notif->cqe.flags |= IORING_CQE_F_COPIED;
> +
As discussed above, should depend on IORING_SEND_ZC_REPORT_USAGE
> io_req_task_complete(notif, locked);
> }
>
> @@ -28,6 +32,11 @@ static void io_uring_tx_zerocopy_callback(struct sk_buff *skb,
> struct io_notif_data *nd = container_of(uarg, struct io_notif_data, uarg);
> struct io_kiocb *notif = cmd_to_io_kiocb(nd);
>
> + if (success && !notif->zc_used && skb)
> + WRITE_ONCE(notif->zc_used, true);
> + else if (!success && !notif->zc_copied)
> + WRITE_ONCE(notif->zc_copied, true);
> +
> if (refcount_dec_and_test(&uarg->refcnt)) {
> notif->io_task_work.func = __io_notif_complete_tw;
> io_req_task_work_add(notif);
> @@ -55,6 +64,7 @@ struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx)
> nd->account_pages = 0;
> nd->uarg.flags = SKBFL_ZEROCOPY_FRAG | SKBFL_DONT_ORPHAN;
> nd->uarg.callback = io_uring_tx_zerocopy_callback;
> + notif->zc_used = notif->zc_copied = false;
> refcount_set(&nd->uarg.refcnt, 1);
> return notif;
> }
>
--
Pavel Begunkov
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