linux-kernel - Re: [RFC PATCH 27/30] Code tagging based latency tracking

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Message-ID: <YxBbFUirdlbXDaZA@hirez.programming.kicks-ass.net>
Date:   Thu, 1 Sep 2022 09:11:17 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     akpm@...ux-foundation.org, kent.overstreet@...ux.dev,
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Subject: Re: [RFC PATCH 27/30] Code tagging based latency tracking

On Tue, Aug 30, 2022 at 02:49:16PM -0700, Suren Baghdasaryan wrote:
> From: Kent Overstreet <kent.overstreet@...ux.dev>
> 
> This adds the ability to easily instrument code for measuring latency.
> To use, add the following to calls to your code, at the start and end of
> the event you wish to measure:
> 
>   code_tag_time_stats_start(start_time);
>   code_tag_time_stats_finish(start_time);
> 
> Stastistics will then show up in debugfs under
> /sys/kernel/debug/time_stats, listed by file and line number.
> 
> Stastics measured include weighted averages of frequency, duration, max
> duration, as well as quantiles.
> 
> This patch also instruments all calls to init_wait and finish_wait,
> which includes all calls to wait_event. Example debugfs output:

How can't you do this with a simple eBPF script on top of
trace_sched_stat_* and friends?