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Date:   Tue, 05 Oct 2021 10:42:07 +0200
From:   Mike Galbraith <efault@....de>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Barry Song <21cnbao@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        Barry Song <song.bao.hua@...ilicon.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: wakeup_affine_weight() is b0rked - was Re: [PATCH 2/2]
 sched/fair: Scale wakeup granularity relative to nr_running

On Tue, 2021-10-05 at 08:47 +0100, Mel Gorman wrote:
> On Mon, Oct 04, 2021 at 11:06:30AM +0200, Mike Galbraith wrote:
> >
> > The mallet below convinced wake_wide() that X waking event threads is
> > something it most definitely should care about.  It's not perfect, can
> > get caught with its pants down, because behavior changes a LOT, but I
> > at least have to work at it a bit to stack tasks to the ceiling.
> >
> > With make -j8 running along with firefox with two tabs, one containing
> > youtube's suggestions of stuff you probably don't want to watch, the
> > other a running clip, if I have the idle tab in focus, and don't drive
> > mouse around, flips decay enough for wake_wide() to lose interest, but
> > just wiggle the mouse, and it starts waking wide. Focus on the running
> > clip, and it continuously wakes wide.  
> >
> > Hacky, but way better behavior.. at this particular testcase.. in this
> > particular box.. at least once :)
> >
>
> Only three machines managed to complete tests overnight. For most
> workloads test, it was neutral or slight improvements. For
> multi-kernbench__netperf-tcp-rr-multipair (kernel compile +
> netperf-tcp-rr combined), there was little to no change.
>
> For the heavy overloaded cases (hackbench again), it was variable. Worst
> improvement was a gain of 1-3%. Best improvement (single socket skylake
> with 8 logical CPUs SMT enabled) was 1%-18% depending on the group
> count.

I wrote up a changelog to remind future me why I bent it up, but I'm
not going to submit it. I'll leave the twiddling to folks who can be
more responsive to possible (spelled probable;) regression reports than
I can be.

	-Mike

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