linux-kernel - Re: [PATCH v2 9/9] Documentation/rtla: Add actions feature

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Message-ID: <CAP4=nvTSycYMGmbJ7nd1Bkp9Rrjn1ojH7VvRo1GCKO5FKm8GZQ@mail.gmail.com>
Date: Wed, 23 Jul 2025 10:30:15 +0200
From: Tomas Glozar <tglozar@...hat.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-trace-kernel@...r.kernel.org, linux-kernel@...r.kernel.org, 
	John Kacur <jkacur@...hat.com>, Luis Goncalves <lgoncalv@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Chang Yin <cyin@...hat.com>, 
	Costa Shulyupin <costa.shul@...hat.com>, Crystal Wood <crwood@...hat.com>, 
	Gabriele Monaco <gmonaco@...hat.com>
Subject: Re: [PATCH v2 9/9] Documentation/rtla: Add actions feature

út 22. 7. 2025 v 17:30 odesílatel Steven Rostedt <rostedt@...dmis.org> napsal:
>
> On Tue, 22 Jul 2025 09:03:24 +0200
> Tomas Glozar <tglozar@...hat.com> wrote:
>
> > Of course, this is just an implementational limitation of the timerlat
> > tracer. If timerlat had an event (like osnoise's "sample_threshold")
> > triggered on threshold overflow and if it is possible to wait on it
> > even without BPF, rtla could wait on that for both BPF and non-BPF
> > mode instead of what it is currently doing.
>
> Right. Is this something you may want?
>

I don't think it is that important. Non-BPF mode is mostly as a
fallback for users of rtla on older kernels which don't have the
osnoise:timerlat_sample trace event. Those are (I assume) mostly users
of LTS distributions who run newer rtla from a container. Adding a new
event wouldn't help in their case.

The only users who would benefit from that are those who don't have
BPF or libbpf. If there is interest from using low-latency actions on
threshold in such settings, I'm not against implementing a threshold
overflow tracepoint and supporting it in rtla for triggering actions
on threshold.

Tomas