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

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Message-ID: <917bb3c8-e084-4790-b0ac-f0433cfca758@intel.com>
Date: Thu, 10 Apr 2025 17:41:45 +0800
From: "Chen, Yu C" <yu.c.chen@...el.com>
To: Swapnil Sapkal <swapnil.sapkal@....com>
CC: <ravi.bangoria@....com>, <mark.rutland@....com>,
	<alexander.shishkin@...ux.intel.com>, <jolsa@...nel.org>,
	<rostedt@...dmis.org>, <vincent.guittot@...aro.org>,
	<adrian.hunter@...el.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>,
	<sshegde@...ux.ibm.com>, <linux-kernel@...r.kernel.org>,
	<linux-perf-users@...r.kernel.org>, <santosh.shukla@....com>,
	<ananth.narayan@....com>, <sandipan.das@....com>, <peterz@...radead.org>,
	<acme@...nel.org>, <james.clark@....com>, <namhyung@...nel.org>,
	<irogers@...gle.com>, <mingo@...hat.com>
Subject: Re: [PATCH v3 0/8] perf sched: Introduce stats tool

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