linux-kernel - Re: [PATCH V5 06/20] trace/osnoise: Allow multiple instances of the same tracer

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Date:   Tue, 26 Oct 2021 09:02:39 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Daniel Bristot de Oliveira <bristot@...nel.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 V5 06/20] trace/osnoise: Allow multiple instances of the
 same tracer

On Tue, 26 Oct 2021 10:38:27 +0200
Daniel Bristot de Oliveira <bristot@...nel.org> wrote:


> >>   * osnoise_register_instance - register a new trace instance
> >>   *
> >> @@ -2048,6 +2066,16 @@ static int osnoise_workload_start(void)
> >>  {
> >>  	int retval;
> >>  
> >> +	/*
> >> +	 * Instances need to be registered after calling workload
> >> +	 * start. Hence, if there is already an instance, the
> >> +	 * workload was already registered. Otherwise, this
> >> +	 * code is on the way to register the first instance,
> >> +	 * and the workload will start.
> >> +	 */
> >> +	if (osnoise_has_registered_instances())
> >> +		return 0;  
> > 
> > Looking at how this is checked before being called, it really should
> > return -1, as it is an error if this is called with instances active.  
> 
> Hum.... maybe my explanation is not good enough. It is not a problem if it is
> called with active instances. It would be an error if the same instance was
> already registered at this point, but that was checked before. Here it is
> checking for other instances that should have enabled the workload.
> 
> Does updating the comment with the one below helps?

No need.


> >> @@ -2096,7 +2131,11 @@ static void osnoise_tracer_start(struct trace_array *tr)
> >>  {
> >>  	int retval;
> >>  
> >> -	if (osnoise_has_registered_instances())
> >> +	/*
> >> +	 * If the instance is already registered, there is no need to
> >> +	 * register it again.
> >> +	 */
> >> +	if (osnoise_instance_registered(tr))

My eyes missed that you removed the osnoise_has_registered_instances() for
the osnoise_instance_registered(tr), and thought you were doing the same
test twice.

My mistake. I need to not review patches at the end of the day when I'm
ready to go to sleep.

-- Steve