From: Jens Axboe <axboe@kernel.dk>
To: Peter Zijlstra <peterz@infradead.org>,
Pavel Begunkov <asml.silence@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>, Ingo Molnar <mingo@redhat.com>,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 0/2] Optimise io_uring completion waiting
Date: Tue, 24 Sep 2019 14:57:01 +0200 [thread overview]
Message-ID: <b66cc383-ceca-b7dd-b3a3-eb998e865cea@kernel.dk> (raw)
In-Reply-To: <20190924114300.GM2332@hirez.programming.kicks-ass.net>
On 9/24/19 5:43 AM, Peter Zijlstra wrote:
> On Tue, Sep 24, 2019 at 02:11:29PM +0300, Pavel Begunkov wrote:
>
>> @@ -2717,15 +2757,18 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
>> return ret;
>> }
>>
>> + iowq.nr_timeouts = atomic_read(&ctx->cq_timeouts);
>> + prepare_to_wait_exclusive(&ctx->wait, &iowq.wq, TASK_INTERRUPTIBLE);
>> + do {
>> + if (io_should_wake(&iowq))
>> + break;
>> + schedule();
>> + if (signal_pending(current))
>> + break;
>> + set_current_state(TASK_INTERRUPTIBLE);
>> + } while (1);
>> + finish_wait(&ctx->wait, &iowq.wq);
>
> It it likely OK, but for paranoia, I'd prefer this form:
>
> for (;;) {
> prepare_to_wait_exclusive(&ctx->wait, &iowq.wq, TASK_INTERRUPTIBLE);
> if (io_should_wake(&iowq))
> break;
> schedule();
> if (signal_pending(current))
> break;
> }
> finish_wait(&ctx->wait, &iowq.wq);
>
> The thing is, if we ever succeed with io_wake_function() (that CPU
> observes io_should_wake()), but when waking here, we do not observe
> is_wake_function() and go sleep again, we might never wake up if we
> don't put ourselves back on the wait-list again.
Might be paranoia indeed, but especially after this change, we don't
expect to make frequent roundtrips there. So better safe than sorry,
I'll make the change.
--
Jens Axboe
next prev parent reply other threads:[~2019-09-24 12:57 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-22 8:08 [PATCH v2 0/2] Optimise io_uring completion waiting Pavel Begunkov (Silence)
2019-09-22 8:08 ` [PATCH v2 1/2] sched/wait: Add wait_threshold Pavel Begunkov (Silence)
2019-09-23 7:19 ` Peter Zijlstra
2019-09-23 16:37 ` Pavel Begunkov
2019-09-23 19:27 ` Peter Zijlstra
2019-09-23 20:23 ` Peter Zijlstra
2019-09-24 6:44 ` Pavel Begunkov
2019-09-22 8:08 ` [PATCH v2 2/2] io_uring: Optimise cq waiting with wait_threshold Pavel Begunkov (Silence)
2019-09-22 15:51 ` [PATCH v2 0/2] Optimise io_uring completion waiting Jens Axboe
2019-09-23 8:35 ` Ingo Molnar
2019-09-23 16:21 ` Pavel Begunkov
2019-09-23 16:32 ` Pavel Begunkov
2019-09-23 20:48 ` Jens Axboe
2019-09-23 23:00 ` Jens Axboe
2019-09-24 7:06 ` Pavel Begunkov
2019-09-24 8:02 ` Jens Axboe
2019-09-24 8:27 ` Jens Axboe
2019-09-24 8:36 ` Jens Axboe
2019-09-24 9:33 ` Pavel Begunkov
2019-09-24 10:11 ` Jens Axboe
2019-09-24 9:49 ` Peter Zijlstra
2019-09-24 10:13 ` Jens Axboe
2019-09-24 10:34 ` Jens Axboe
2019-09-24 11:11 ` Pavel Begunkov
2019-09-24 11:15 ` Jens Axboe
2019-09-24 11:23 ` Pavel Begunkov
2019-09-24 13:13 ` Jens Axboe
2019-09-24 17:33 ` Pavel Begunkov
2019-09-24 17:46 ` Jens Axboe
2019-09-24 18:28 ` Pavel Begunkov
2019-09-24 19:32 ` Jens Axboe
2019-09-24 11:43 ` Peter Zijlstra
2019-09-24 12:57 ` Jens Axboe [this message]
2019-09-24 11:33 ` Peter Zijlstra
2019-09-24 9:20 ` Pavel Begunkov
2019-09-24 10:09 ` Jens Axboe
2019-09-24 9:21 ` Pavel Begunkov
2019-09-24 10:09 ` Jens Axboe
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