linux-kernel - Re: [PATCH 2/2] sched/fair: Always propagate runnable_load

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Message-ID: <20170425210810.GB20255@wtj.duckdns.org>
Date:   Tue, 25 Apr 2017 14:08:10 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mike Galbraith <efault@....de>, Paul Turner <pjt@...gle.com>,
        Chris Mason <clm@...com>, kernel-team@...com
Subject: Re: [PATCH 2/2] sched/fair: Always propagate runnable_load_avg

On Tue, Apr 25, 2017 at 11:49:41AM -0700, Tejun Heo wrote:
> > I have run a quick test with your patches and schbench on my platform.
> > I haven't been able to reproduce your regression but my platform is
> > quite different from yours (only 8 cores without SMT)
> > But most importantly, the parent cfs_rq->runnable_load_avg never
> > reaches 0 (or almost 0) when it is idle. Instead, it still has a
> > runnable_load_avg (this is not due to rounding computation) whereas
> > runnable_load_avg should be 0
>  
> Heh, let me try that out.  Probably a silly mistake somewhere.

This is from the follow-up patch.  I was confused.  Because we don't
propagate decays, we still should decay the runnable_load_avg;
otherwise, we end up accumulating errors in the counter.  I'll drop
the last patch.

Thanks.

-- 
tejun