From: Peter Zijlstra <[email protected]>
To: Oleg Nesterov <[email protected]>
Cc: "Jens Axboe" <[email protected]>,
"Carter Li 李通洲" <[email protected]>,
"Pavel Begunkov" <[email protected]>,
io-uring <[email protected]>
Subject: Re: [ISSUE] The time cost of IOSQE_IO_LINK
Date: Tue, 18 Feb 2020 16:07:56 +0100 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
On Tue, Feb 18, 2020 at 03:56:46PM +0100, Oleg Nesterov wrote:
> On 02/18, Peter Zijlstra wrote:
> >
> > But this has me wondering about task_work_run(), as it is it will
> > unconditionally take pi_lock,
>
> because spin_unlock_wait() was removed ;) task_work_run() doesn't
> really need to take pi_lock at all.
Right.
> > --- a/kernel/task_work.c
> > +++ b/kernel/task_work.c
> > @@ -93,16 +93,20 @@ void task_work_run(void)
> > struct callback_head *work, *head, *next;
> >
> > for (;;) {
> > + work = READ_ONCE(task->task_work);
> > + if (!work)
> > + break
>
> This is wrong if PF_EXITING is set, in this case we must set
> task->task_works = work_exited.
Indeed!
> > +
> > /*
> > * work->func() can do task_work_add(), do not set
> > * work_exited unless the list is empty.
> > */
> > raw_spin_lock_irq(&task->pi_lock);
> > do {
> > - work = READ_ONCE(task->task_works);
> > - head = !work && (task->flags & PF_EXITING) ?
> > - &work_exited : NULL;
> > - } while (cmpxchg(&task->task_works, work, head) != work);
> > + head = NULL;
> > + if (unlikely(!work && (task->flags & PF_EXITING)))
> > + head = &work_exited;
> > + } while (!try_cmpxchg(&task->task_works, &work, head));
> > raw_spin_unlock_irq(&task->pi_lock);
> >
> > if (!work)
>
> otherwise I think this is correct, but how about the patch below?
> Then this code can be changed to use try_cmpxchg().
Works for me. Thanks!
next prev parent reply other threads:[~2020-02-18 15:08 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-12 16:31 [ISSUE] The time cost of IOSQE_IO_LINK Carter Li 李通洲
2020-02-12 17:11 ` Jens Axboe
2020-02-12 17:22 ` Jens Axboe
2020-02-12 17:29 ` Jens Axboe
2020-02-13 0:33 ` Carter Li 李通洲
2020-02-13 15:08 ` Pavel Begunkov
2020-02-13 15:14 ` Jens Axboe
2020-02-13 15:51 ` Carter Li 李通洲
2020-02-14 1:25 ` Carter Li 李通洲
2020-02-14 2:45 ` Jens Axboe
2020-02-14 5:03 ` Jens Axboe
2020-02-14 15:32 ` Peter Zijlstra
2020-02-14 15:47 ` Jens Axboe
2020-02-14 16:18 ` Jens Axboe
2020-02-14 17:52 ` Jens Axboe
2020-02-14 20:44 ` Jens Axboe
2020-02-15 0:16 ` Carter Li 李通洲
2020-02-15 1:10 ` Jens Axboe
2020-02-15 1:25 ` Carter Li 李通洲
2020-02-15 1:27 ` Jens Axboe
2020-02-15 6:01 ` Jens Axboe
2020-02-15 6:32 ` Carter Li 李通洲
2020-02-15 15:11 ` Jens Axboe
2020-02-16 19:06 ` Pavel Begunkov
2020-02-16 22:23 ` Jens Axboe
2020-02-17 10:30 ` Pavel Begunkov
2020-02-17 19:30 ` Jens Axboe
2020-02-16 23:06 ` Jens Axboe
2020-02-16 23:07 ` Jens Axboe
2020-02-17 12:09 ` Peter Zijlstra
2020-02-17 16:12 ` Jens Axboe
2020-02-17 17:16 ` Jens Axboe
2020-02-17 17:46 ` Peter Zijlstra
2020-02-17 18:16 ` Jens Axboe
2020-02-18 13:13 ` Peter Zijlstra
2020-02-18 14:27 ` [PATCH] asm-generic/atomic: Add try_cmpxchg() fallbacks Peter Zijlstra
2020-02-18 14:40 ` Peter Zijlstra
2020-02-20 10:30 ` Will Deacon
2020-02-20 10:37 ` Peter Zijlstra
2020-02-20 10:39 ` Will Deacon
2020-02-18 14:56 ` [ISSUE] The time cost of IOSQE_IO_LINK Oleg Nesterov
2020-02-18 15:07 ` Oleg Nesterov
2020-02-18 15:38 ` Peter Zijlstra
2020-02-18 16:33 ` Jens Axboe
2020-02-18 15:07 ` Peter Zijlstra [this message]
2020-02-18 15:50 ` [PATCH] task_work_run: don't take ->pi_lock unconditionally Oleg Nesterov
2020-02-20 16:39 ` Peter Zijlstra
2020-02-20 17:22 ` Oleg Nesterov
2020-02-20 17:49 ` Peter Zijlstra
2020-02-21 14:52 ` Oleg Nesterov
2020-02-24 18:47 ` Jens Axboe
2020-02-28 19:17 ` Jens Axboe
2020-02-28 19:25 ` Peter Zijlstra
2020-02-28 19:28 ` Jens Axboe
2020-02-28 20:06 ` Peter Zijlstra
2020-02-28 20:15 ` Jens Axboe
2020-02-18 16:46 ` [ISSUE] The time cost of IOSQE_IO_LINK Jens Axboe
2020-02-18 16:52 ` Jens Axboe
2020-02-18 13:13 ` Peter Zijlstra
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