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Message-ID: <97ee06c66fe0d900e3e0c4145ef9d33457ab3c65.camel@gmx.de>
Subject: Re: [PATCH 2/2] sched/fair: Scale wakeup granularity relative to
 nr_running
From:   Mike Galbraith <efault@gmx.de>
To:     Mel Gorman <mgorman@techsingularity.net>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Valentin Schneider <valentin.schneider@arm.com>,
        Aubrey Li <aubrey.li@linux.intel.com>,
        Barry Song <song.bao.hua@hisilicon.com>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        LKML <linux-kernel@vger.kernel.org>
Date:   Wed, 22 Sep 2021 16:04:01 +0200
In-Reply-To: <20210922132002.GX3959@techsingularity.net>
References: <20210920142614.4891-1-mgorman@techsingularity.net>
         <20210920142614.4891-3-mgorman@techsingularity.net>
         <22e7133d674b82853a5ee64d3f5fc6b35a8e18d6.camel@gmx.de>
         <20210921103621.GM3959@techsingularity.net>
         <ea2f9038f00d3b4c0008235079e1868145b47621.camel@gmx.de>
         <20210922132002.GX3959@techsingularity.net>
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On Wed, 2021-09-22 at 14:20 +0100, Mel Gorman wrote:
> On Wed, Sep 22, 2021 at 07:22:20AM +0200, Mike Galbraith wrote:
> >
> > Watching 'while sleep 1; do clear;tail trace; done' with nothing but a
> > kbuild running is like watching top.=C2=A0 There's enough stacking dur=
ing
> > routine use of my desktop box that it runs into the tick granularity
> > wall pretty much continuously, so 'overload' may want redefining.
> >
>
> Ok, that's pretty convincing. You didn't mention if there were
> interactivity glitches but it's possible.

No, I didn't notice a thing.  That's not surprising given the amount of
scheduling going on.  The stack depth surprised me a bit though.

X-2230    [005] d..5.  2162.123029: wakeup_gran: runnable:6 wakee:QXcbEven=
tQueue:2695 CPU5
X-2230    [005] d..5.  2162.123035: wakeup_gran: runnable:7 wakee:QXcbEven=
tQueue:2656 CPU5
X-2230    [005] d..5.  2162.123046: wakeup_gran: runnable:8 wakee:QXcbEven=
tQueue:5876 CPU5
X-2230    [005] d..5.  2162.123049: wakeup_gran: runnable:9 wakee:QXcbEven=
tQueue:5355 CPU5
X-2230    [005] d..5.  2162.123083: wakeup_gran: runnable:10 wakee:QXcbEve=
ntQueue:2723 CPU5
X-2230    [005] d..5.  2162.123097: wakeup_gran: runnable:11 wakee:QXcbEve=
ntQueue:2630 CPU5
X-2230    [005] d..5.  2162.123208: wakeup_gran: runnable:12 wakee:QXcbEve=
ntQueue:2760 CPU5

That CPU# on the end is task_cpu(). Lord knows why X wakes all those,
but with no SD_BALANCE_WAKE, a busy box and all those having last lived
on waker's CPU, the resulting construct.. probably doesn't very closely
resemble what the programmer had in mind when threading.

	-Mike