linux-kernel - Re: [PATCH] sched/cpufreq: don't trigger cpufreq update w/o real rt/deadline tasks running

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Message-ID: <CANRm+CzGm5axJC_y=rqhmi=DLkfpXfo2NLzFyRyjeZE89Aty4Q@mail.gmail.com>
Date:	Thu, 21 Apr 2016 06:24:18 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Ingo Molnar <mingo@...hat.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Wanpeng Li <wanpeng.li@...mail.com>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Steve Muckle <steve.muckle@...aro.org>
Subject: Re: [PATCH] sched/cpufreq: don't trigger cpufreq update w/o real
 rt/deadline tasks running

2016-04-20 22:01 GMT+08:00 Peter Zijlstra <peterz@...radead.org>:
> On Wed, Apr 20, 2016 at 02:32:35AM +0200, Rafael J. Wysocki wrote:
>> On Monday, April 18, 2016 01:51:24 PM Wanpeng Li wrote:
>> > Sometimes update_curr() is called w/o tasks actually running, it is
>> > captured by:
>> >     u64 delta_exec = rq_clock_task(rq) - curr->se.exec_start;
>> > We should not trigger cpufreq update in this case for rt/deadline
>> > classes, and this patch fix it.
>> >
>> > Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
>>
>> The signed-off-by tag should agree with the From: header.  One way to achieve
>> that is to add an extra From: line at the start of the changelog.
>>
>> That said, this looks like a good catch that should go into 4.6 to me.
>>
>> Peter, what do you think?
>
> I'm confused by the Changelog. *what* ?

Sometimes .update_curr hook is called w/o tasks actually running, it is
captured by:

        u64 delta_exec = rq_clock_task(rq) - curr->se.exec_start;

We should not trigger cpufreq update in this case for rt/deadline
classes, and this patch fix it.

Regards,
Wanpeng Li