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

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Message-ID: <b4dbc5f4-a379-4824-9898-95271728ab03@amd.com>
Date: Wed, 18 Sep 2024 14:15:48 +0530
From: "Sapkal, Swapnil" <swapnil.sapkal@....com>
To: <20240916164722.1838-1-ravi.bangoria@....com>, Ravi Bangoria
	<ravi.bangoria@....com>
CC: <irogers@...gle.com>, <namhyung@...nel.org>, <acme@...nel.org>,
	<peterz@...radead.org>, <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 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.
>