linux-kernel - Re: [PATCH v6 00/20] Proxy Execution: A generalized form of Priority Inheritance v6

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Message-ID: <5d9c994140e7375979bc3d58a216c8eb261275a9.camel@arm.com>
Date:   Wed, 13 Dec 2023 16:20:20 +0000
From:   Metin Kaya <Metin.Kaya@....com>
To:     "jstultz@...gle.com" <jstultz@...gle.com>,
        "kprateek.nayak@....com" <kprateek.nayak@....com>
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Subject: Re: [PATCH v6 00/20] Proxy Execution: A generalized form of Priority
 Inheritance v6

On Wed, 2023-12-13 at 12:07 +0530, K Prateek Nayak wrote:
> Hello John,
>
> I may have some data that might help you debug a potential
> performance
> issue mentioned below.
>
> On 11/7/2023 1:04 AM, John Stultz wrote:
> > [..snip..]
> >
> > Performance:
> > —----------
> > This patch series switches mutexes to use handoff mode rather
> > than optimistic spinning. This is a potential concern where locks
> > are under high contention. However, earlier performance analysis
> > (on both x86 and mobile devices) did not see major regressions.
> > That said, Chenyu did report a regression[3], which I’ll need to
> > look further into.
>
> I too see this as the most notable regression. Some of the other
> benchmarks I've tested (schbench, tbench, netperf, ycsb-mongodb,
> DeathStarBench) show little to no difference when running with Proxy
> Execution, however sched-messaging sees a 10x blowup in the runtime.
> (taskset -c 0-7,128-125 perf bench sched messaging -p -t -l 100000 -g
> 1)

I observe similar regression. Total time of `taskset -c 0-5,6-11 perf
bench sched messaging -p -t -l 100000 -g 1` increases from 13.964 secs
to 184.866 secs on my test machine. Other perf sched benchmarks look
OK.

>
> While investigating, I drew up the runqueue length when running
> sched-messaging pinned to 1CCX (CPUs 0-7,128-125 on my 3rd Generation
> EPYC system) using the following bpftrace script that dumps it csv
> format:
>

[snip]

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