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

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Message-ID: <57180293.1040809@intel.com>
Date:	Thu, 21 Apr 2016 00:28:35 +0200
From:	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
To:	Wanpeng Li <kernellwp@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Ingo Molnar <mingo@...hat.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

On 4/21/2016 12:24 AM, Wanpeng Li wrote:
> 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.

That's what you wrote in the changelog, no need to repeat that.

I guess Peter is asking for more details, though.  I actually would like 
to get some more details here too.  Like an example of when the 
situation in question actually happens.

Thanks,
Rafael