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Date: Tue, 23 Aug 2016 16:13:41 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Yuyang Du <yuyang.du@intel.com>, Ingo Molnar <mingo@kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Benjamin Segall <bsegall@google.com>, Paul Turner <pjt@google.com>,
        Morten Rasmussen <morten.rasmussen@arm.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Matt Fleming <matt@codeblueprint.co.uk>,
        Mike Galbraith <umgwanakikbuti@gmail.com>
Subject: Re: [PATCH v1 00/10] Optimize sched avgs computation and implement
 flat util hierarchy
Message-ID: <20160823141341.GP10153@twins.programming.kicks-ass.net>
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On Tue, Aug 23, 2016 at 03:28:19PM +0200, Vincent Guittot wrote:
> I still wonder if using a flat util hierarchy is the right solution to
> solve this problem with utilization and task group. I have noticed
> exact same issues with load that generates weird task placement
> decision and i think that we should probably try to solve both wrong
> behavior with same mechanism. but this is not possible with flat
> hierarchy for load
> 
> Let me take an example.
> TA is a always running task on CPU1 in group /root/level1/
> TB wakes up on CPU0 and moves TA into group /root/level2/
> Even if TA stays on CPU1, runnable_load_avg of CPU1 root cfs rq will become 0.

Because while we migrate the load_avg on /root/level2, we do not
propagate the load_avg up the hierarchy?

And always propagating everyrthing up will indeed also fix the
utilization issue.

Of course, doing that propagation has its costs..

Didn't you post a patch doing just this a while ago?