From: Oleg Nesterov <oleg@redhat.com>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Chris Mason <chris.mason@oracle.com>,
Frank Rowand <frank.rowand@am.sony.com>,
Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
Mike Galbraith <efault@gmx.de>, Paul Turner <pjt@google.com>,
Jens Axboe <axboe@kernel.dk>, Yong Zhang <yong.zhang0@gmail.com>,
linux-kernel@vger.kernel.org
Subject: Re: [RFC][PATCH 16/17] sched: Move the second half of ttwu() to the remote cpu
Date: Tue, 4 Jan 2011 17:06:12 +0100 [thread overview]
Message-ID: <20110104160612.GA9177@redhat.com> (raw)
In-Reply-To: <1294155781.2016.160.camel@laptop>
On 01/04, Peter Zijlstra wrote:
>
> On Tue, 2011-01-04 at 16:18 +0100, Oleg Nesterov wrote:
>
> > > I don't think so, nobody should be migrating a TASK_WAKING task.
> >
> > I am not sure...
> >
> > Suppose that p was TASK_INTERRUPTIBLE and p->on_rq == 1 before, when
> > set_cpus_allowed_ptr() was called. To simplify, suppose that
> > the caller is preempted right after it drops p->pi_lock and before
> > it does stop_one_cpu(migration_cpu_stop).
> >
> > After that p can complete chedule() and deactivate itself.
> >
> > Now, try_to_wake_up() can set TASK_WAKING, choose another CPU,
> > and do ttwu_queue_remote().
> >
> > Finally, the caller of set_cpus_allowed_ptr() resumes and
> > schedules migration_cpu_stop.
>
> But __migrate_task() will then find !p->on_rq and not actually do
> anything.
But if it races with ttwu_do_activate() (which can hold another
rq->lock != rq_src/rq_dest), it can check p->on_rq after
activate_task() was already called.
But I think this no longer matters,
> > It is very possible I missed something, but what is the new
> > locking rules for set_task_cpu() anyway? I mean, which rq->lock
> > it needs?
>
> In the patches I just posted: set_task_cpu(p, cpu) callers need to
> either hold task_rq(p)->lock (the old rq) or p->pi_lock.
Yes, thanks, I already noticed v4, and at first glance 11/18 plus
set_task_cpu() in try_to_wake_up() should close the problems...
Oleg.
next prev parent reply other threads:[~2011-01-04 16:14 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-12-24 12:23 [RFC][PATCH 00/17] sched: Reduce runqueue lock contention -v3 Peter Zijlstra
2010-12-24 12:23 ` [RFC][PATCH 01/17] sched: Always provide p->on_cpu Peter Zijlstra
2010-12-24 12:23 ` [RFC][PATCH 02/17] mutex: Use p->on_cpu for the adaptive spin Peter Zijlstra
2010-12-24 12:23 ` [RFC][PATCH 03/17] sched: Change the ttwu success details Peter Zijlstra
2010-12-24 12:23 ` [RFC][PATCH 04/17] sched: Clean up ttwu stats Peter Zijlstra
2010-12-24 12:23 ` [RFC][PATCH 05/17] x86: Optimize arch_spin_unlock_wait() Peter Zijlstra
2010-12-24 18:26 ` Linus Torvalds
2011-01-03 11:32 ` Peter Zijlstra
2011-01-04 6:45 ` Nick Piggin
2011-01-05 19:14 ` [RFC][PATCH] spinlock: Kill spin_unlock_wait() Peter Zijlstra
2011-01-05 19:26 ` Oleg Nesterov
2011-01-05 19:43 ` Linus Torvalds
2011-01-06 9:32 ` Peter Zijlstra
2011-01-06 10:38 ` Nick Piggin
2011-01-06 18:26 ` Peter Zijlstra
2011-01-07 21:01 ` Tejun Heo
2011-01-07 21:13 ` Jeff Garzik
2011-01-07 21:33 ` Tejun Heo
2010-12-24 12:23 ` [RFC][PATCH 06/17] sched: Provide p->on_rq Peter Zijlstra
2010-12-29 14:14 ` Yong Zhang
2010-12-24 12:23 ` [RFC][PATCH 07/17] sched: Serialize p->cpus_allowed and ttwu() using p->pi_lock Peter Zijlstra
2010-12-29 14:20 ` Yong Zhang
2011-01-03 11:12 ` Peter Zijlstra
2010-12-24 12:23 ` [RFC][PATCH 08/17] sched: Drop the rq argument to sched_class::select_task_rq() Peter Zijlstra
2010-12-29 14:31 ` Yong Zhang
2011-01-03 11:16 ` Peter Zijlstra
2011-01-03 14:59 ` Oleg Nesterov
2011-01-03 15:21 ` Peter Zijlstra
2011-01-03 15:49 ` Oleg Nesterov
2011-01-03 16:35 ` Peter Zijlstra
2011-01-03 16:41 ` Peter Zijlstra
2011-01-04 7:27 ` Yong Zhang
2011-01-04 12:34 ` Peter Zijlstra
2011-01-04 5:59 ` Yong Zhang
2011-01-04 13:00 ` Peter Zijlstra
2011-01-03 18:05 ` Oleg Nesterov
2011-01-04 13:01 ` Peter Zijlstra
2010-12-24 12:23 ` [RFC][PATCH 09/17] sched: Remove rq argument to sched_class::task_waking() Peter Zijlstra
2010-12-24 12:23 ` [RFC][PATCH 10/17] sched: Add TASK_WAKING to task_rq_lock Peter Zijlstra
2010-12-24 12:23 ` [RFC][PATCH 11/17] sched: Delay task_contributes_to_load() Peter Zijlstra
2010-12-24 12:23 ` [RFC][PATCH 12/17] sched: Also serialize ttwu_local() with p->pi_lock Peter Zijlstra
2011-01-03 17:32 ` Oleg Nesterov
2011-01-09 23:11 ` Tejun Heo
2010-12-24 12:23 ` [RFC][PATCH 13/17] sched: Remove rq->lock from the first half of ttwu() Peter Zijlstra
2010-12-24 12:23 ` [RFC][PATCH 14/17] sched: Remove rq argument to ttwu_stat() Peter Zijlstra
2010-12-29 14:40 ` Yong Zhang
2011-01-03 11:20 ` Peter Zijlstra
2010-12-24 12:23 ` [RFC][PATCH 15/17] sched: Rename ttwu_post_activation Peter Zijlstra
2010-12-24 12:23 ` [RFC][PATCH 16/17] sched: Move the second half of ttwu() to the remote cpu Peter Zijlstra
2011-01-03 14:36 ` [RFC][PATCH] sembench: add stddev to the burn stats Peter Zijlstra
2011-01-04 14:28 ` [RFC][PATCH 16/17] sched: Move the second half of ttwu() to the remote cpu Oleg Nesterov
2011-01-04 14:47 ` Peter Zijlstra
2011-01-04 15:18 ` Oleg Nesterov
2011-01-04 15:43 ` Peter Zijlstra
2011-01-04 16:06 ` Oleg Nesterov [this message]
2010-12-24 12:23 ` [RFC][PATCH 17/17] sched: Sort hotplug vs ttwu queueing Peter Zijlstra
2010-12-29 14:51 ` Yong Zhang
2011-01-03 11:21 ` Peter Zijlstra
2010-12-24 13:15 ` [RFC][PATCH 00/17] sched: Reduce runqueue lock contention -v3 Peter Zijlstra
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