linux-kernel - Re: [RFC PATCH 3/3] sched: Implement shared wakequeue in CFS

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Message-ID: <20230621023534.GA236337@ziqianlu-dell>
Date:   Wed, 21 Jun 2023 10:35:34 +0800
From:   Aaron Lu <aaron.lu@...el.com>
To:     David Vernet <void@...ifault.com>
CC:     Peter Zijlstra <peterz@...radead.org>,
        <linux-kernel@...r.kernel.org>, <mingo@...hat.com>,
        <juri.lelli@...hat.com>, <vincent.guittot@...aro.org>,
        <rostedt@...dmis.org>, <dietmar.eggemann@....com>,
        <bsegall@...gle.com>, <mgorman@...e.de>, <bristot@...hat.com>,
        <vschneid@...hat.com>, <joshdon@...gle.com>,
        <roman.gushchin@...ux.dev>, <tj@...nel.org>, <kernel-team@...a.com>
Subject: Re: [RFC PATCH 3/3] sched: Implement shared wakequeue in CFS

On Tue, Jun 20, 2023 at 12:36:26PM -0500, David Vernet wrote:
> On Fri, Jun 16, 2023 at 08:53:38AM +0800, Aaron Lu wrote:
> > I also tried that on the 18cores/36threads/LLC Skylake and the contention
> > is indeed much smaller than UDP_RR:
> > 
> >      7.30%     7.29%  [kernel.vmlinux]      [k]      native_queued_spin_lock_slowpath
> > 
> > But I wouldn't say it's entirely gone. Also consider Skylake has a lot
> > fewer cores per LLC than later Intel servers like Icelake and Sapphire
> > Rapids and I expect things would be worse on those two machines.
> 
> I cannot reproduce this contention locally, even on a slightly larger

With netperf client number equal to nr_cpu?

> Skylake. Not really sure what to make of the difference here. Perhaps
> it's because you're running with CONFIG_SCHED_CORE=y? What is the

Yes I had that config on but I didn't tag any tasks or groups.

> change in throughput when you run the default workload on your SKL?

The throughput dropped a little with SWQUEUE:

                 avg_throughput    native_queued_spin_lock_slowpath%
NO_SWQUEUE:      9528.061111111108      0.09%
SWQUEUE:         8984.369722222222      8.05%

avg_throughput: average throughput of all netperf client's throughput,
higher is better.

I run this workload like this:
"
netserver

for i in `seq 72`; do
        netperf -l 60 -n 72 -6 &
done

sleep 30
perf record -ag -e cycles:pp -- sleep 5 &

wait
"
(the '-n 72' should be redundant but I just keep it there)

Thanks,
Aaron