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Date: Mon, 29 Aug 2016 09:37:31 +0800
From: Yuyang Du <yuyang.du@intel.com>
To: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>,
        Peter Zijlstra <peterz@infradead.org>, 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>,
        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: <20160829013731.GH3273@intel.com>
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On Tue, Aug 23, 2016 at 04:39:51PM +0100, Dietmar Eggemann wrote:
> On 23/08/16 15:45, Vincent Guittot wrote:
> > On 23 August 2016 at 16:13, Peter Zijlstra <peterz@infradead.org> wrote:
> >> 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?
> > 
> > yes. At now, the load of a cfs_rq and the load of its sched_entity
> > that represents it at parent level are disconnected
> 
> I guess you say 'disconnected' because cfs_rq and se (w/ cfs_rq eq.
> se->my_q) are now independent pelt signals where as before the rewrite
> they were 'connected' for load via __update_tg_runnable_avg(),
> __update_group_entity_contrib() in __update_entity_load_avg_contrib()
> and for utilization via 'se->avg.utilization_avg_contrib =
> group_cfs_rq(se)->utilization_load_avg' in
> __update_entity_utilization_avg_contrib().
 
I don't understand what exactly "disconnected" means, but with respect to
group_entity's load_avg, nothing is changed essentially:

group_entity_load_avg = my_cfs_rq_load_avg / tg_load_avg * tg_shares