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From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: Steve Muckle <smuckle@google.com>, Wanpeng Li <kernellwp@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Miguel de Dios <migueldedios@google.com>,
	Ingo Molnar <mingo@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>,
	kernel-team@android.com, Todd Kjos <tkjos@google.com>,
	Paul Turner <pjt@google.com>,
	quentin.perret@arm.com, Patrick Bellasi <Patrick.Bellasi@arm.com>,
	Chris.Redpath@arm.com,
	Morten Rasmussen <Morten.Rasmussen@arm.com>,
	John Dias <joaodias@google.com>,
	Wanpeng Li <wanpengli@tencent.com>
Subject: Re: [PATCH] sched/fair: vruntime should normalize when switching from fair
Date: Fri, 28 Sep 2018 19:35:53 +0200	[thread overview]
Message-ID: <2cee0f7c-023d-7b20-0a19-c2a4427625d9@arm.com> (raw)
In-Reply-To: <c0ec8322-4256-d8ae-0978-25ab44e34d68@google.com>

On 09/28/2018 06:10 PM, Steve Muckle wrote:
> On 09/27/2018 05:43 PM, Wanpeng Li wrote:
>>>> On your CPU4:
>>>> scheduler_ipi()
>>>>    -> sched_ttwu_pending()
>>>>         -> ttwu_do_activate()    => p->sched_remote_wakeup should be
>>>> false, so ENQUEUE_WAKEUP is set, ENQUEUE_MIGRATED is not
>>>>              -> ttwu_activate()
>>>>                   -> activate_task()
>>>>                        -> enqueue_task()
>>>>                             -> enqueue_task_fair()
>>>>                                  -> enqueue_entity()
>>>>                                       bool renorm = !(flags &
>>>> ENQUEUE_WAKEUP) || (flags & ENQUEUE_MIGRATE)
>>>> so renorm is false in enqueue_entity(), why you mentioned that the
>>>> cfs_rq->min_vruntime is still added to the se->vruntime in
>>>> enqueue_task_fair()?
>>>
>>> Maybe this is a misunderstanding on my side but didn't you asked me to
>>> '... Could you point out when the fair rq's min_vruntime is added to the
>>> task's vruntime in your *later* scenario? ...'
>>
>> Yeah, if the calltrace above and my analysis is correct, then the fair
>> rq's min_vruntime will not be added to the task's vruntime in your
>> *later* scenario, which means that your patch is not necessary.
> 
> In the scenario I observed, the task is not waking - it is running and 
> being deboosted from priority inheritance, transitioning from RT to CFS.
> 
> Dietmar and I both were able to reproduce the issue with the testcase I 
> posted earlier in this thread.

Correct, and with the same testcase I got this call stack in this scenario:

[   35.588509] CPU: 1 PID: 2926 Comm: fair_task Not tainted 
4.18.0-rc6-00052-g11b7dafa2edb-dirty #5
[   35.597217] Hardware name: ARM Juno development board (r0) (DT)
[   35.603080] Call trace:
[   35.605509]  dump_backtrace+0x0/0x168
[   35.609138]  show_stack+0x24/0x30
[   35.612424]  dump_stack+0xac/0xe4
[   35.615710]  enqueue_task_fair+0xae0/0x11c0
[   35.619854]  rt_mutex_setprio+0x5a0/0x628
[   35.623827]  mark_wakeup_next_waiter+0x7c/0xc8
[   35.628228]  __rt_mutex_futex_unlock+0x30/0x50
[   35.632630]  do_futex+0x74c/0xb28
[   35.635912]  sys_futex+0x118/0x198
[   35.639280]  el0_svc_naked+0x30/0x34

[...]


  parent reply	other threads:[~2018-09-28 17:36 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
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 [this message]
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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