linux-kernel - Re: [PATCH v8 2/2] sched/fair: Introduce SIS_CURRENT to wake up short task on current CPU

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Date:   Tue, 02 May 2023 04:51:51 +0200
From:   Mike Galbraith <efault@....de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Chen Yu <yu.c.chen@...el.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Tim Chen <tim.c.chen@...el.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>,
        K Prateek Nayak <kprateek.nayak@....com>,
        Abel Wu <wuyun.abel@...edance.com>,
        Yicong Yang <yangyicong@...ilicon.com>,
        "Gautham R . Shenoy" <gautham.shenoy@....com>,
        Honglei Wang <wanghonglei@...ichuxing.com>,
        Len Brown <len.brown@...el.com>,
        Chen Yu <yu.chen.surf@...il.com>,
        Tianchen Ding <dtcccc@...ux.alibaba.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Josh Don <joshdon@...gle.com>,
        kernel test robot <yujie.liu@...el.com>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>,
        Aaron Lu <aaron.lu@...el.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 2/2] sched/fair: Introduce SIS_CURRENT to wake up
 short task on current CPU

On Mon, 2023-05-01 at 20:49 +0200, Peter Zijlstra wrote:
> On Mon, May 01, 2023 at 05:32:05PM +0200, Mike Galbraith wrote:
> > On Mon, 2023-05-01 at 15:48 +0200, Peter Zijlstra wrote:
> > >
> > > Throughput  646.55 MB/sec   2 clients   2 procs  max_latency=0.104 ms
> > > Throughput 1361.06 MB/sec   5 clients   5 procs  max_latency=0.100 ms
> > > Throughput 1889.82 MB/sec  10 clients  10 procs  max_latency=0.154 ms
> > > Throughput 2406.57 MB/sec  20 clients  20 procs  max_latency=3.667 ms
> > > Throughput 2318.00 MB/sec  40 clients  40 procs  max_latency=0.390 ms
> > > Throughput 2384.85 MB/sec  80 clients  80 procs  max_latency=1.371 ms
> > >
> > >
> > > So what's going on here? I don't see anything exciting happening at the
> > > 40 mark. At the same time, I can't seem to reproduce Mike's latency pile
> > > up either :/
> >
> > Are you running tbench in the GUI so the per second output stimulates
> > assorted goo?  I'm using KDE fwtw.
>
> Nah, the IVB-EP is headless, doesn't even have systemd on, still running
> sysvinit.

Turns out load distribution on Yu's box wasn't going wonky way early
after all, so WA_WEIGHT's evil side is off topic wrt $subject.  Hohum.

	-Mike