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

Sapkal, Swapnil
2025-04-10T10:29:33Z

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