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Message-ID: <32495917a028e9c70b75357029a87ca593378dde.camel@trillion01.com>
Subject: Re: [PATCH v4] io_uring: reduce latency by reissueing the operation
From:   Olivier Langlois <olivier@trillion01.com>
To:     Pavel Begunkov <asml.silence@gmail.com>,
        Jens Axboe <axboe@kernel.dk>, io-uring@vger.kernel.org,
        linux-kernel@vger.kernel.org
Date:   Tue, 22 Jun 2021 15:05:55 -0400
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         <678deb93-c4a5-5a14-9687-9e44f0f00b5a@gmail.com>
         <7c47078a-9e2d-badf-a47d-1ca78e1a3253@gmail.com>
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On Tue, 2021-06-22 at 19:01 +0100, Pavel Begunkov wrote:
> On 6/22/21 6:54 PM, Pavel Begunkov wrote:
> > On 6/22/21 1:17 PM, Olivier Langlois wrote:
> > > 
> > 
> > > ?static bool __io_poll_remove_one(struct io_kiocb *req,
> > > @@ -6437,6 +6445,7 @@ static void __io_queue_sqe(struct io_kiocb
> > > *req)
> > > ????????struct io_kiocb *linked_timeout =
> > > io_prep_linked_timeout(req);
> > > ????????int ret;
> > > ?
> > > +issue_sqe:
> > > ????????ret = io_issue_sqe(req,
> > > IO_URING_F_NONBLOCK|IO_URING_F_COMPLETE_DEFER);
> > > ?
> > > ????????/*
> > > @@ -6456,12 +6465,16 @@ static void __io_queue_sqe(struct
> > > io_kiocb *req)
> > > ????????????????????????io_put_req(req);
> > > ????????????????}
> > > ????????} else if (ret == -EAGAIN && !(req->flags &
> > > REQ_F_NOWAIT)) {
> > > -???????????????if (!io_arm_poll_handler(req)) {
> > > +???????????????switch (io_arm_poll_handler(req)) {
> > > +???????????????case IO_APOLL_READY:
> > > +???????????????????????goto issue_sqe;
> > > +???????????????case IO_APOLL_ABORTED:
> > > ????????????????????????/*
> > > ???????????????????????? * Queued up for async execution, worker
> > > will release
> > > ???????????????????????? * submit reference when the iocb is
> > > actually submitted.
> > > ???????????????????????? */
> > > ????????????????????????io_queue_async_work(req);
> > > +???????????????????????break;
> > 
> > Hmm, why there is a new break here? It will miscount
> > @linked_timeout
> > if you do that. Every io_prep_linked_timeout() should be matched
> > with
> > io_queue_linked_timeout().
> 
> Never mind, I said some nonsense and apparently need some coffee

but this is a pertinant question, imho. I guess that you could get away
without it since it is the last case of the switch statement... I am
not sure what kernel coding standard says about that.

However, I can tell you that there was also a break statement at the
end of the case for IO_APOLL_READY and checkpatch.pl did complain about
it saying that it was useless since it was following a goto statement.
Therefore, I did remove that one.

checkpatch.pl did remain silent about the other remaining break. Hence
this is why I left it there.

Greetings,