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

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Date: Thu, 9 May 2024 14:49:56 +0530
From: Aditya Gupta <adityag@...ux.ibm.com>
To: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
Cc: peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        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

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,
Aditya Gupta