linux-kernel - Re: [PATCH V4 05/19] trace/osnoise: Allow multiple instances of the same tracer

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Message-ID: <7770e301-178f-725a-aa7f-b674b41ed20c@kernel.org>
Date:   Mon, 25 Oct 2021 10:08:39 +0200
From:   Daniel Bristot de Oliveira <bristot@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Ingo Molnar <mingo@...hat.com>, Tom Zanussi <zanussi@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Clark Williams <williams@...hat.com>,
        John Kacur <jkacur@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        linux-rt-users@...r.kernel.org, linux-trace-devel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4 05/19] trace/osnoise: Allow multiple instances of the
 same tracer

On 10/23/21 04:47, Steven Rostedt wrote:
> On Thu, 21 Oct 2021 14:56:43 +0200
> Daniel Bristot de Oliveira <bristot@...nel.org> wrote:
> 
>> Allow more than one instance of the same tracer. The workload will
>> start when the first trace_array (instance) is registered and will
>> stop when the last instance is unregistered.
>>
> 
> 
>> Osnoise and timerlat are still mutually exclusive because of the
>> different behavior of the osnoise: tracepoints.
> 
> I don't understand what the above means, or how it is relative to this
> commit?

osnoise and timerlat tracers share a lot of code, including the osnoise: events.

However, the osnoise: events have different behavior depending on which tracer
is enabled. So, while this patch allows the same tracer to run in multiple
instances (e.g., two instances running osnoise), it still does not allow
instances of timerlat and osnoise in parallel (e.g., one timerlat and osnoise).

Should I add the text above to the log?

It is possible to extend the current behavior to allow concurrent osnoise and
timerlat tracers to run on different CPUs. For instance, osnoise on cpu 0,1 and
timerlat on cpu 2,3. This is on my to-do list, but it is not necessary for now.

-- Daniel

> -- Steve
>