Date: Mon, 6 May 2013 13:10:41 +0200
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Paul Turner <pjt@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>, Alex Shi <alex.shi@intel.com>,
        Ingo Molnar <mingo@redhat.com>, Thomas Gleixner <tglx@linutronix.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Borislav Petkov <bp@alien8.de>, Namhyung Kim <namhyung@kernel.org>,
        Mike Galbraith <efault@gmx.de>,
        Morten Rasmussen <morten.rasmussen@arm.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Preeti U Murthy <preeti@linux.vnet.ibm.com>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        LKML <linux-kernel@vger.kernel.org>, Mel Gorman <mgorman@suse.de>,
        Rik van Riel <riel@redhat.com>,
        Michael Wang <wangyun@linux.vnet.ibm.com>
Subject: Re: [PATCH v5 5/7] sched: compute runnable load avg in cpu_load and
 cpu_avg_load_per_task
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On Mon, May 06, 2013 at 03:33:45AM -0700, Paul Turner wrote:
> Yeah, most of the rationale is super hand-wavy; especially the fairly
> arbitrary choice of periods (e.g. busy_idx vs newidle).
> 
> I think the other rationale is:
>   For smaller indicies (e.g. newidle) we speed up response time by
> also cutting motion out of the averages.
> 
> The runnable_avgs themselves actually have a fair bit of history in
> them already (50% is last 32ms); but given that they don't need to be
> cut-off to respond to load being migrated I'm guessing we could
> actually potentially get by with just "instaneous" and "use averages"
> where appropriate?

Sure,. worth a try. If things fall over we can always look at it again.

> We always end up having to re-pick/tune them based on a variety of
> workloads; if we can eliminate them I think it would be a win.

Agreed, esp. the plethora of weird idx things we currently have. If we need to
re-introduce something it would likely only be the busy case and for that we
can immediately link to the balance interval or so.


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