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

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Message-ID: <af4000b6-02c7-4160-8207-57f34239bd49@linux.ibm.com>
Date: Tue, 17 Sep 2024 16:27:36 +0530
From: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
To: Ravi Bangoria <ravi.bangoria@....com>
Cc: irogers@...gle.com, namhyung@...nel.org, acme@...nel.org,
        peterz@...radead.org, swapnil.sapkal@....com, yu.c.chen@...el.com,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        jolsa@...nel.org, rostedt@...dmis.org, vincent.guittot@...aro.org,
        bristot@...hat.com, adrian.hunter@...el.com, james.clark@....com,
        kan.liang@...ux.intel.com, gautham.shenoy@....com,
        kprateek.nayak@....com, juri.lelli@...hat.com,
        yangjihong@...edance.com, void@...ifault.com, tj@...nel.org,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        santosh.shukla@....com, ananth.narayan@....com, sandipan.das@....com,
        mingo@...hat.com, Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
Subject: Re: [PATCH 0/5] perf sched: Introduce stats tool

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!

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.