From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752468AbcEKAxJ (ORCPT <rfc822;w@1wt.eu>);
	Tue, 10 May 2016 20:53:09 -0400
Received: from mail-oi0-f66.google.com ([209.85.218.66]:35288 "EHLO
	mail-oi0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751382AbcEKAxH (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Tue, 10 May 2016 20:53:07 -0400
MIME-Version: 1.0
In-Reply-To: <CAO2XSW5oUD6S5iZ2Ms9OTnOOpzuAwzctv_=WpDdx6pSv5gArXw@mail.gmail.com>
References: <CAO2XSW5oUD6S5iZ2Ms9OTnOOpzuAwzctv_=WpDdx6pSv5gArXw@mail.gmail.com>
Date: Wed, 11 May 2016 08:53:05 +0800
Message-ID: <CANRm+CwGEsjJKnjiMPVOTjPUjYLK2-WFJhVvQ44qOi6SM16RVw@mail.gmail.com>
Subject: Re: PROBLEM: Scheduling latency not respected in CFS with HRTICK enabled
From: Wanpeng Li <kernellwp@gmail.com>
To: Tomasz Grabiec <tgrabiec@scylladb.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>
Content-Type: text/plain; charset=UTF-8
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

2016-05-06 23:43 GMT+08:00 Tomasz Grabiec <tgrabiec@scylladb.com>:
[...]
> prev_comm=python prev_pid=873 prev_prio=120 prev_state=R ==>
> next_comm=python next_pid=874 next_prio=120
>   python   874 [002] 3273334.932741: probe:hrtick: (ffffffff8109b430)
>   python   874 [002] 3273334.932742: sched:sched_stat_runtime:
> comm=python pid=874 runtime=503174 [ns] vruntime=1549788942230752 [ns]

hrtick fire after almost 0.5ms(the time slice process 874 get).

>   python   874 [002] 3273334.932743: sched:sched_stat_runtime:
> comm=python pid=874 runtime=948 [ns] vruntime=1549788942231700 [ns]
>   python   874 [002] 3273334.936240: probe:scheduler_tick: (ffffffff810a1f30)
>   python   874 [002] 3273334.936241: sched:sched_stat_runtime:
> comm=python pid=874 runtime=3497530 [ns] vruntime=1549788945729230
> [ns]

continue to run another 3.4ms until next normal scheduler tick fire.

>   python   874 [002] 3273334.936249: sched:sched_stat_runtime:
> comm=python pid=874 runtime=8553 [ns] vruntime=1549788945737783 [ns]
>   python   874 [002] 3273334.936250: sched:sched_stat_wait:
> comm=python pid=873 delay=4010205 [ns]
>   python   874 [002] 3273334.936250: probe:hrtick_start: (ffffffff8109f4f0)
>   python   874 [002] 3273334.936251: sched:sched_switch:
> prev_comm=python prev_pid=874 prev_prio=120 prev_state=R ==>
> next_comm=python next_pid=873 next_prio=120

So the process 874 continue to run util next scheduler fick event if
hrtick has already fired. I think Peterz can give any light.

Ping Peterz :-)

Regards,
Wanpeng Li