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From: Peter Zijlstra <peterz@infradead.org>
To: Jann Horn <jannh@google.com>
Cc: Jens Axboe <axboe@kernel.dk>, io-uring <io-uring@vger.kernel.org>,
	Glauber Costa <glauber@scylladb.com>,
	Pavel Begunkov <asml.silence@gmail.com>
Subject: Re: [PATCH 7/9] io_uring: add per-task callback handler
Date: Fri, 21 Feb 2020 17:12:02 +0100	[thread overview]
Message-ID: <20200221161202.GY14897@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAG48ez3Bc6gCVX7Gd2mFDR=ktGE0M_H+s6pHao2NjUrbxub20w@mail.gmail.com>

On Fri, Feb 21, 2020 at 04:02:36PM +0100, Jann Horn wrote:
> On Fri, Feb 21, 2020 at 3:49 PM Jens Axboe <axboe@kernel.dk> wrote:
> > On 2/21/20 3:47 AM, Peter Zijlstra wrote:

> > > But I thought to understand that these sched_work things were only
> > > queued on tasks that were stuck waiting on POLL (or it's io_uring
> > > equivalent). Earlier patches were explicitly running things from
> > > io_cqring_wait(), which might have given me this impression.
> >
> > No, that is correct.
> 
> Really? I was pretty sure that io_uring does not force the calling
> thread to block on the io_uring operations to continue; and isn't that
> the whole point?
> 
> I think that when Peter says "stuck waiting on POLL", he really means
> "blocked in the context of sys_io_uring_enter() and can't go
> anywhere";

Exactly.

> while I think you interpret it as "has pending POLL work
> queued up in the background and may decide to wait for it in
> sys_io_uring_enter(), but might also be doing anything else".

In which case it can hit schedule() at some random point before it gets
to io_uring_cqring_wait().

  reply	other threads:[~2020-02-21 16:12 UTC|newest]

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-20 20:31 [PATCHSET 0/9] io_uring: use polled async retry Jens Axboe
2020-02-20 20:31 ` [PATCH 1/9] io_uring: consider any io_read/write -EAGAIN as final Jens Axboe
2020-02-20 20:31 ` [PATCH 2/9] io_uring: io_accept() should hold on to submit reference on retry Jens Axboe
2020-02-20 20:31 ` [PATCH 3/9] sched: move io-wq/workqueue worker sched in/out into helpers Jens Axboe
2020-02-20 20:31 ` [PATCH 4/9] task_work_run: don't take ->pi_lock unconditionally Jens Axboe
2020-02-20 20:31 ` [PATCH 5/9] kernel: abstract out task work helpers Jens Axboe
2020-02-20 21:07   ` Peter Zijlstra
2020-02-20 21:08     ` Jens Axboe
2020-02-20 20:31 ` [PATCH 6/9] sched: add a sched_work list Jens Axboe
2020-02-20 21:17   ` Peter Zijlstra
2020-02-20 21:53     ` Jens Axboe
2020-02-20 22:02       ` Jens Axboe
2020-02-20 20:31 ` [PATCH 7/9] io_uring: add per-task callback handler Jens Axboe
2020-02-20 22:02   ` Jann Horn
2020-02-20 22:14     ` Jens Axboe
2020-02-20 22:18       ` Jens Axboe
2020-02-20 22:25         ` Jann Horn
2020-02-20 22:23       ` Jens Axboe
2020-02-20 22:38         ` Jann Horn
2020-02-20 22:56           ` Jens Axboe
2020-02-20 22:58             ` Jann Horn
2020-02-20 23:02               ` Jens Axboe
2020-02-20 22:23       ` Jann Horn
2020-02-20 23:00         ` Jens Axboe
2020-02-20 23:12           ` Jann Horn
2020-02-20 23:22             ` Jens Axboe
2020-02-21  1:29               ` Jann Horn
2020-02-21 17:32                 ` Jens Axboe
2020-02-21 19:24                   ` Jann Horn
2020-02-21 20:18                     ` Jens Axboe
2020-02-20 22:56     ` Jann Horn
2020-02-21 10:47     ` Peter Zijlstra
2020-02-21 14:49       ` Jens Axboe
2020-02-21 15:02         ` Jann Horn
2020-02-21 16:12           ` Peter Zijlstra [this message]
2020-02-21 16:23         ` Peter Zijlstra
2020-02-21 20:13           ` Jens Axboe
2020-02-21 13:51   ` Pavel Begunkov
2020-02-21 14:50     ` Jens Axboe
2020-02-21 18:30       ` Pavel Begunkov
2020-02-21 19:10         ` Jens Axboe
2020-02-21 19:22           ` Pavel Begunkov
2020-02-23  6:00           ` Jens Axboe
2020-02-23  6:26             ` Jens Axboe
2020-02-23 11:02               ` Pavel Begunkov
2020-02-23 14:49                 ` Jens Axboe
2020-02-23 14:58                   ` Jens Axboe
2020-02-23 15:07                     ` Jens Axboe
2020-02-23 18:04                       ` Pavel Begunkov
2020-02-23 18:06                         ` Jens Axboe
2020-02-23 17:55                   ` Pavel Begunkov
2020-02-20 20:31 ` [PATCH 8/9] io_uring: mark requests that we can do poll async in io_op_defs Jens Axboe
2020-02-20 20:31 ` [PATCH 9/9] io_uring: use poll driven retry for files that support it Jens Axboe

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