Re: [PATCH v3 0/8] perf sched: Introduce stats tool

[Sapkal, Swapnil]

Hi Chenyu,

On 4/10/2025 3:11 PM, Chen, Yu C wrote:
> Hi Swapnil,
>
> On 3/11/2025 8:02 PM, Swapnil Sapkal wrote:
> > MOTIVATION
> > ----------
> >
> > Existing `perf sched` is quite exhaustive and provides lot of insights
> > into scheduler behavior but it quickly becomes impractical to use for
> > long running or scheduler intensive workload. For ex, `perf sched record`
> > has ~7.77% overhead on hackbench (with 25 groups each running 700K loops
> > on a 2-socket 128 Cores 256 Threads 3rd Generation EPYC Server), and it
> > generates huge 56G perf.data for which perf takes ~137 mins to prepare
> > and write it to disk [1].
> >
> > Unlike `perf sched record`, which hooks onto set of scheduler tracepoints
> > and generates samples on a tracepoint hit, `perf sched stats record` takes
> > snapshot of the /proc/schedstat file before and after the workload, i.e.
> > there is almost zero interference on workload run. Also, it takes very
> > minimal time to parse /proc/schedstat, convert it into perf samples and
> > save those samples into perf.data file. Result perf.data file is much
> > smaller. So, overall `perf sched stats record` is much more light weight
> > compare to `perf sched record`.
> >
> > We, internally at AMD, have been using this (a variant of this, known as
> > "sched-scoreboard"[2]) and found it to be very useful to analyse impact
> > of any scheduler code changes[3][4]. Prateek used v2[5] of this patch
> > series to report the analysis[6][7].
> >
> > Please note that, this is not a replacement of perf sched record/report.
> > The intended users of the new tool are scheduler developers, not regular
> > users.
> >
> > USAGE
> > -----
> >
> >    # perf sched stats record
> >    # perf sched stats report
> >    # perf sched stats diff
>
> May I know the status of this patch set? I tested it on a 96 cores system and it works as expected in general.

Thank you for testing the patch set. I am working on v4 based on the Namhyung's suggestions.

> One nit question:
> Is perf.data and perf.data.old the default files
> for comparison if no files are provided in
> perf sched stats diff?

Yes, if no files are provided to `perf sched stats diff`, it will take perf.data and perf.data.old as defaults.

> thanks,
> Chenyu
--
Thanks and Regards,
Swapnil