linux-kernel - Re: [PATCH RFC 1/3] perf/core: add logic to collect off-cpu sample

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Message-ID: <CAD2QZ9YQ6n_6J+bq+wNxS5bGuAOsLkSiicigan84qaD+xrjS3Q@mail.gmail.com>
Date: Sun, 14 Jul 2024 21:53:10 +0530
From: Ajay Kaher <ajay.kaher@...adcom.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: mingo@...hat.com, acme@...nel.org, namhyung@...nel.org, 
	mark.rutland@....com, rostedt@...dmis.org, alexander.shishkin@...ux.intel.com, 
	jolsa@...nel.org, irogers@...gle.com, adrian.hunter@...el.com, 
	kan.liang@...ux.intel.com, yangjihong1@...wei.com, zegao2021@...il.com, 
	leo.yan@...ux.dev, asmadeus@...ewreck.org, siyanteng@...ngson.cn, 
	sunhaiyong@...ngson.cn, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org, alexey.makhalov@...adcom.com, 
	vasavi.sirnapalli@...adcom.com, 
	Vamsi Krishna Brahmajosyula <vamsi-krishna.brahmajosyula@...adcom.com>, nadav.amit@...il.com
Subject: Re: [PATCH RFC 1/3] perf/core: add logic to collect off-cpu sample

On Fri, Jul 12, 2024 at 3:19 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Thu, Jul 11, 2024 at 05:46:17PM +0530, Ajay Kaher wrote:
> > following logics has been added to collect the off-cpu sample:
> >
> > - 'task_pt_regs(current)' has been used to capture registers
> >   status off-cpu sample.
> >
> > - off-cpu time represent the time period for which the target
> >   process not occupying the cpu cycles. And calculate as:
> >
> >   off-cpu time = swap-in time - swap-out time
> >
>
> I have absolutely no idea what you're trying to do :/ The above does not
> constitute a comprehensible Changelog.

Sorry Peter, it’s sched-in/out (not swap-in/out).

'Perf record' captures on-cpu samples at frequency which is specified by
the user ( i.e. time period to collect sample is NSEC_PER_SEC / freq).

This patch is to collect the off_cpu sample and time period of off_cpu
sample is calculated based upon the time when target task was sched_out
to sched_in, as:

 off-cpu time period = sched_in time - sched-out time

-Ajay