Re: [PATCH 0/5] perf sched: Introduce stats tool

From: Sapkal, Swapnil
Date: Wed Sep 18 2024 - 04:50:22 EST


Hi Vineeth,

Thank you for testing the series.

On 9/17/2024 4:27 PM, Madadi Vineeth Reddy wrote:
Hi Ravi,

On 16/09/24 22:17, Ravi Bangoria 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

per.data file is empty after the record.

Error:
The perf.data data has no samples!

I am not able to reproduce this error on my system. Can you please share `/proc/schedstat` file from your system? What was the base kernel you applied this on?

--
Thanks And Regards,
Swapnil

Thanks and Regards
Madadi Vineeth Reddy

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].

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.