linux-kernel - Re: [RFC PATCH 2/3] sched: Introduce Window-Assisted CPU utilization Tracking

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Date:   Fri, 28 Oct 2016 00:58:16 -0700
From:   Vikram Mulukutla <markivx@...eaurora.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Srivatsa Vaddagiri <vatsa@...eaurora.org>,
        Steve Muckle <steve.muckle@...aro.org>,
        Olav Haugan <ohaugan@...eaurora.org>,
        Syed Rameez Mustafa <rameezmustafa@...eaurora.org>,
        Joonwoo Park <joonwoop@...eaurora.org>,
        Pavankumar Kondeti <pkondeti@...eaurora.org>,
        Saravana Kannan <skannan@...eaurora.org>,
        Bryan Huntsman <bryanh@...eaurora.org>,
        Juri Lelli <juri.lelli@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Chris Redpath <chris.redpath@....com>,
        Robin Randhawa <robin.randhawa@....com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Todd Kjos <tkjos@...gle.com>,
        Srinath Sridharan <srinathsr@...gle.com>,
        Andres Oportus <andresoportus@...gle.com>,
        Leo Yan <leo.yan@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Vikram Mulukutla <markivx@...eauorora.org>
Subject: Re: [RFC PATCH 2/3] sched: Introduce Window-Assisted CPU utilization
 Tracking

On 2016-10-28 00:43, Peter Zijlstra wrote:
> On Fri, Oct 28, 2016 at 12:10:41AM -0700, Vikram Mulukutla wrote:
>> +u64 walt_ktime_clock(void)
>> +{
>> +	if (unlikely(walt_ktime_suspended))
>> +		return ktime_to_ns(ktime_last);
>> +	return ktime_get_ns();
>> +}
> 
>> +static int walt_suspend(void)
>> +{
>> +	ktime_last = ktime_get();
>> +	walt_ktime_suspended = true;
>> +	return 0;
>> +}
> 
> No, ktime_get() will not be used in the scheduler. Imagine the joy if
> that thing ends up being the HPET.

Agreed, this is an artifact from the full implementation that feeds into 
the
interactive governor, and thus both needed to use the same time source. 
It
shall go away.