linux-kernel - Re: [RFC PATCH 0/3] sched: Introduce Window Assisted Load Tracking

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Date:   Fri, 28 Oct 2016 00:55:52 -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 0/3] sched: Introduce Window Assisted Load Tracking

On 2016-10-28 00:29, Peter Zijlstra wrote:
> On Fri, Oct 28, 2016 at 12:10:39AM -0700, Vikram Mulukutla wrote:
>> 
>> We propose Window-Assisted Load Tracking (WALT) as an alternative or 
>> additional
>> load tracking scheme in lieu of or along with PELT, one that in our 
>> estimation
>> better tracks task demand and CPU utilization especially for use cases 
>> on
>> mobile devices. WALT was conceived by Srivatsa Vaddagiri to provide 
>> better
>> perf-per-watt numbers on asymmetric CPU (frequency and/or IPC) 
>> implementations,
>> (specifically on Qualcomm Snapgdragon chipsets running Android) and 
>> its metrics
>> have been used to guide task placement and p-state selection (load 
>> balancing
>> in CFS still uses PELT statistics). WALT is now present in the 
>> android-common
>> kernel as well.
> 
> And how come we only learn of it after its already shipping? Isn't that
> arse backwards?

Yes, but also we were not confident that it would be close to being 
acceptable
upstream since it was intricately tied to our HMP scheduler. However now 
that
more parties including the folks at ARM are interested, and given that 
EAS
exists and schedutil was merged into mainline, we felt it the right time
to try and introduce the concept. In general we are seriously trying to 
get
more things upstream and converge.