From: Peter Zijlstra <peterz@infradead.org>
To: Steve Muckle <smuckle@google.com>
Cc: Miguel de Dios <migueldedios@google.com>,
Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org, kernel-team@android.com,
Todd Kjos <tkjos@google.com>, Paul Turner <pjt@google.com>,
Quentin Perret <quentin.perret@arm.com>,
Patrick Bellasi <Patrick.Bellasi@arm.com>,
Chris Redpath <Chris.Redpath@arm.com>,
Morten Rasmussen <Morten.Rasmussen@arm.com>,
John Dias <joaodias@google.com>
Subject: Re: [PATCH] sched/fair: vruntime should normalize when switching from fair
Date: Mon, 27 Aug 2018 13:14:58 +0200 [thread overview]
Message-ID: <20180827111458.GB24124@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <ae94fb88-646b-1d82-b61d-103792965dbf@google.com>
On Fri, Aug 24, 2018 at 02:24:48PM -0700, Steve Muckle wrote:
> On 08/24/2018 02:47 AM, Peter Zijlstra wrote:
> > > > On 08/17/2018 11:27 AM, Steve Muckle wrote:
> >
> > > > > When rt_mutex_setprio changes a task's scheduling class to RT,
> > > > > we're seeing cases where the task's vruntime is not updated
> > > > > correctly upon return to the fair class.
> >
> > > > > Specifically, the following is being observed:
> > > > > - task is deactivated while still in the fair class
> > > > > - task is boosted to RT via rt_mutex_setprio, which changes
> > > > > the task to RT and calls check_class_changed.
> > > > > - check_class_changed leads to detach_task_cfs_rq, at which point
> > > > > the vruntime_normalized check sees that the task's state is TASK_WAKING,
> > > > > which results in skipping the subtraction of the rq's min_vruntime
> > > > > from the task's vruntime
> > > > > - later, when the prio is deboosted and the task is moved back
> > > > > to the fair class, the fair rq's min_vruntime is added to
> > > > > the task's vruntime, even though it wasn't subtracted earlier.
> >
> > I'm thinking that is an incomplete scenario; where do we get to
> > TASK_WAKING.
>
> Yes there's a missing bit of context here at the beginning that the task to
> be boosted had already been put into TASK_WAKING.
See, I'm confused...
The only time TASK_WAKING is visible, is if we've done a remote wakeup
and it's 'stuck' on the remote wake_list. And in that case we've done
migrate_task_rq_fair() on it.
So by the time either rt_mutex_setprio() or __sched_setscheduler() get
to calling check_class_changed(), under both pi_lock and rq->lock, the
vruntime_normalized() thing should be right.
So please detail the exact scenario. Because I'm not seeing it.
next prev parent reply other threads:[~2018-08-27 11:15 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-17 18:27 [PATCH] sched/fair: vruntime should normalize when switching from fair Steve Muckle
2018-08-20 23:54 ` Miguel de Dios
2018-08-23 16:52 ` Dietmar Eggemann
2018-08-24 6:54 ` Juri Lelli
2018-08-24 21:17 ` Steve Muckle
2018-09-06 23:25 ` Dietmar Eggemann
2018-09-07 7:16 ` Juri Lelli
2018-09-07 7:58 ` Vincent Guittot
2018-09-11 6:24 ` Dietmar Eggemann
2018-08-24 9:32 ` Peter Zijlstra
2018-08-24 9:47 ` Peter Zijlstra
2018-08-24 21:24 ` Steve Muckle
2018-08-27 11:14 ` Peter Zijlstra [this message]
2018-08-28 14:53 ` Dietmar Eggemann
2018-08-29 10:54 ` Dietmar Eggemann
2018-08-29 11:59 ` Peter Zijlstra
2018-08-29 15:33 ` Dietmar Eggemann
2018-08-31 22:24 ` Steve Muckle
2018-09-26 9:50 ` Wanpeng Li
2018-09-26 22:38 ` Dietmar Eggemann
2018-09-27 1:19 ` Wanpeng Li
2018-09-27 13:22 ` Dietmar Eggemann
2018-09-28 0:43 ` Wanpeng Li
2018-09-28 16:10 ` Steve Muckle
2018-09-28 16:45 ` Joel Fernandes
2018-09-28 17:35 ` Dietmar Eggemann
2018-09-29 1:07 ` Wanpeng Li
2018-09-28 17:11 ` Dietmar Eggemann
2018-09-28 16:43 ` Joel Fernandes
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