Re: [PATCH] perf: add new option '--workload-attr' to set workload sched_policy/priority/mask

[Ian Rogers]

On Fri, Jul 14, 2023 at 12:19 AM Changbin Du <changbin.du@xxxxxxxxxx> 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 perf 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.sh:
https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/tests/shell/stat.sh?h=perf-tools-next

Thanks,
Ian

> --
> Cheers,
> Changbin Du