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

Chen, Yu C
2025-04-10T09:42:20Z

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.

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?

thanks,
Chenyu