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From:   Ian Rogers <irogers@google.com>
Date:   Wed, 19 Jul 2023 09:55:39 -0700
Message-ID: <CAP-5=fV49y9y8Q3-3rhACMQJiQ+nAh0RfysT8bhpJ5_AOqLScw@mail.gmail.com>
Subject: Re: [PATCH] perf: add new option '--workload-attr' to set workload sched_policy/priority/mask
To:     Changbin Du <changbin.du@huawei.com>
Cc:     Adrian Hunter <adrian.hunter@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@kernel.org>,
        Namhyung Kim <namhyung@kernel.org>,
        linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org
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On Fri, Jul 14, 2023 at 12:19=E2=80=AFAM Changbin Du <changbin.du@huawei.co=
m> wrote:
>
> On Fri, Jul 14, 2023 at 10:06:31AM +0300, Adrian Hunter wrote:
> > On 13/07/23 11:58, Changbin Du wrote:
> > > To get consistent benchmarking results, sometimes we need to set the
> > > sched_policy/priority/mask of the workload to reduce system noise.
> > >
> > > For example, CPU binding is required on big.little system.
> > >
> > >   $ perf stat -r 10 -- taskset -c 0 ls
> > >
> > > Nevertheless, the 'taskset' is also counted here.
> > >
> > > To get away of the middleman, this adds a new option '--workload-attr=
' to
> > > do the same jobs for stat and record commands.
> > >
> > >   $ sudo perf stat --workload-attr fifo,40,0x1 -- ls
> > >
> > > Above will make 'ls' run on CPU #0 with fifo scheduler and realtime
> > > priority is 40.
> >
> > Aren't there ways to set up a process then start perf using -p <pid>
> > then let the process continue.
> >
> By that you need a mechanism to pause the new spawnned process and wait p=
erf to
> attach. Or setup the sched properties by the app itself. But sometimes we=
 just
> simply want to run the app through and measure some events. With
> --workload-attr, we do not need extra setup works.

To my naive eyes this looks to be a broadly useful addition. Some thoughts:
 - "cpu-mask" as the command line argument name, this is "-C" and
"--cpu" elsewhere, so perhaps just "cpu" as the mask is perhaps
confusing.
 - could we get a test? Perhaps add a case to tools/perf/tests/shell/stat.s=
h:
https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tr=
ee/tools/perf/tests/shell/stat.sh?h=3Dperf-tools-next

Thanks,
Ian

> --
> Cheers,
> Changbin Du