linux-kernel - Re: [PATCH] perf sched: Rename switches to count and add usage description, options for latency

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Date: Fri, 10 May 2024 11:11:36 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Aditya Gupta <adityag@...ux.ibm.com>
Cc: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>, peterz@...radead.org,
	mingo@...hat.com, namhyung@...nel.org, mark.rutland@....com,
	alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
	irogers@...gle.com, adrian.hunter@...el.com,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf sched: Rename switches to count and add usage
 description, options for latency

On Thu, May 09, 2024 at 02:49:56PM +0530, Aditya Gupta wrote:
> Hello vineeth,
> 
> On Thu, Mar 28, 2024 at 02:30:05PM +0530, Madadi Vineeth Reddy wrote:
> > Rename 'Switches' to 'Count' and document metrics shown for perf
> > sched latency output. Also add options possible with perf sched
> > latency.
> > 
> > Initially, after seeing the output of 'perf sched latency', the term
> > 'Switches' seemed like it's the number of context switches-in for a
> > particular task, but upon going through the code, it was observed that
> > it's actually keeping track of number of times a delay was calculated so
> > that it is used in calculation of the average delay.
> > 
> > Actually, the switches here is a subset of number of context switches-in
> > because there are some cases where the count is not incremented in
> > switch-in handler 'add_sched_in_event'. For example when a task is
> > switched-in while it's state is not ready to run(!= THREAD_WAIT_CPU).
> > 
> > commit d9340c1db3f5 ("perf sched: Display time in milliseconds, reorganize
> > output") changed it from the original count to switches.
> > 
> > So, renamed switches to count to make things a bit more clearer and
> > added the metrics description of latency in the document.
> > 
> > Signed-off-by: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
> 
> Makes sense to me. 'Switches' seems to be context switches, so it might
> be better kept as 'Count' only.
> 
> Hence,
> 
> Reviewed-by: Aditya Gupta <adityag@...ux.ibm.com>


Thanks, applied to perf-tools-next,

- Arnaldo

- Arnaldo