From: Oleg Nesterov <oleg@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>,
mingo@kernel.org, john.stultz@linaro.org, dimitrysh@google.com,
linux-kernel@vger.kernel.org, Davidlohr Bueso <dbueso@suse.de>
Subject: Re: [PATCH v2 2/3] locking/percpu-rwsem: Rework writer block/wake to not use wait-queues
Date: Mon, 5 Dec 2016 18:19:17 +0100 [thread overview]
Message-ID: <20161205171916.GC13035@redhat.com> (raw)
In-Reply-To: <20161205083605.GQ3092@twins.programming.kicks-ass.net>
On 12/05, Peter Zijlstra wrote:
>
> > + for (;;) {
> > + set_current_state(TASK_UNINTERRUPTIBLE);
> > +
> > + if (readers_active_check(sem))
> > + break;
> > +
> > + schedule();
> > + }
> > +
> > + rcu_assign_pointer(sem->writer, NULL);
>
> And this one does not, and the value being NULL this actually reverts to
> WRITE_ONCE().
Do we really care? We do not even need WRITE_ONCE() afaics, this is like
__set_current_state(TASK_RUNNING) after the main loop. We can't avoid the
spurious wakeups anyway after return from percpu_down_write().
Oleg.
next prev parent reply other threads:[~2016-12-05 17:19 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-18 18:54 [PATCH -tip 0/3] locking/percpu-rwsem: writer-side optimizations Davidlohr Bueso
2016-11-18 18:54 ` [PATCH 1/3] locking/percpu-rwsem: Move text file into Documentation/locking/ Davidlohr Bueso
2016-11-18 18:54 ` [PATCH 2/3] locking/percpu-rwsem: Replace bulky wait-queues with swait Davidlohr Bueso
2016-11-21 12:55 ` Oleg Nesterov
2016-11-21 17:26 ` Davidlohr Bueso
2016-12-03 2:18 ` [PATCH v2 2/3] locking/percpu-rwsem: Rework writer block/wake to not use wait-queues Davidlohr Bueso
2016-12-05 8:36 ` Peter Zijlstra
2016-12-05 11:26 ` Oleg Nesterov
2016-12-05 11:32 ` Oleg Nesterov
2016-12-05 17:37 ` Davidlohr Bueso
2016-12-05 17:19 ` Oleg Nesterov [this message]
2016-12-05 17:13 ` Oleg Nesterov
2016-11-18 18:54 ` [PATCH 3/3] locking/percpu-rwsem: Avoid unnecessary writer wakeups Davidlohr Bueso
2016-11-21 12:23 ` Oleg Nesterov
2016-11-21 12:29 ` Peter Zijlstra
2016-11-21 12:47 ` Oleg Nesterov
2016-11-21 15:07 ` Oleg Nesterov
2016-11-22 3:59 ` Davidlohr Bueso
2016-11-23 14:43 ` Oleg Nesterov
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