From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Corey Minyard <cminyard@mvista.com>
Cc: linux-rt-users <linux-rt-users@vger.kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Tejun Heo <tj@kernel.org>, Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: Warning from swake_up_all in 4.14.15-rt13 non-RT
Date: Thu, 8 Mar 2018 18:41:03 +0100 [thread overview]
Message-ID: <20180308174103.mduy5qq2ttlcvig3@linutronix.de> (raw)
In-Reply-To: <1704d817-8fb9-ce8f-1aa1-fe6e8b0c3919@mvista.com>
On 2018-03-07 09:45:29 [-0600], Corey Minyard wrote:
> > I have no idea what is the wisest thing to do here. The obvious fix
> > would be to use the irqsafe() variant here and not drop the lock between
> > wake ups. That is essentially what swake_up_all_locked() does which I
> > need for the completions (and based on some testing most users have one
> > waiter except during PM and some crypto code).
> > It is probably no comparison to wake_up_q() (which does multiple wake
> > ups without a context switch) but then we did this before like that.
> >
> > Preferably we would have a proper list_splice() and some magic in the
> > "early" dequeue part that works.
> >
>
> Maybe just modify the block code to run the swake_up_all() call in a
> workqueue
> or tasklet? If you think that works, I'll create a patch, test it, and
> submit it if
> all goes well.
It will work but I don't think pushing this into workqueue/tasklet is a
good idea. You want to wakeup all waiters on waitqueue X (probably one
waiter) and instead there is one one wakeup + ctx-switch which does the
final wakeup.
But now I had an idea: swake_up_all() could iterate over list and
instead performing wakes it would just wake_q_add() the tasks. Drop the
lock and then wake_up_q(). So in case there is wakeup pending and the
task removed itself from the list then the task may observe a spurious
wakeup.
> Thanks,
>
> -corey
Sebastian
next prev parent reply other threads:[~2018-03-08 17:41 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-05 15:08 Warning from swake_up_all in 4.14.15-rt13 non-RT Corey Minyard
2018-03-06 17:46 ` Sebastian Andrzej Siewior
2018-03-06 22:51 ` Corey Minyard
2018-03-07 15:45 ` Corey Minyard
2018-03-08 17:41 ` Sebastian Andrzej Siewior [this message]
2018-03-08 19:54 ` Corey Minyard
2018-03-09 11:04 ` Sebastian Andrzej Siewior
2018-03-09 13:29 ` Corey Minyard
2018-03-09 14:58 ` Sebastian Andrzej Siewior
2018-03-09 16:03 ` Corey Minyard
2018-03-09 17:46 ` Peter Zijlstra
2018-03-09 20:25 ` Sebastian Andrzej Siewior
2018-03-09 22:26 ` Peter Zijlstra
2018-03-12 10:51 ` Sebastian Andrzej Siewior
2018-03-12 13:27 ` Peter Zijlstra
2018-03-12 14:11 ` Sebastian Andrzej Siewior
2018-03-12 14:29 ` Peter Zijlstra
2018-03-12 19:51 ` Sebastian Andrzej Siewior
2018-03-13 18:40 ` [RT PATCH 1/2] Revert "block: blk-mq: Use swait" Sebastian Andrzej Siewior
2018-03-13 18:42 ` [RT PATCH 2/2] block: blk-mq: move blk_queue_usage_counter_release() into process context Sebastian Andrzej Siewior
2018-03-13 20:10 ` Peter Zijlstra
2018-03-14 15:23 ` Sebastian Andrzej Siewior
2018-03-09 22:02 ` Warning from swake_up_all in 4.14.15-rt13 non-RT Corey Minyard
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