Re: [PATCH v3 01/17] tools/rv: Do not skip idle in trace

[Gabriele Monaco <gmonaco@redhat.com>]

On Wed, 2025-07-16 at 14:41 +0200, Peter Zijlstra wrote:
> On Wed, Jul 16, 2025 at 02:18:28PM +0200, Gabriele Monaco wrote:
> > On Wed, 2025-07-16 at 13:50 +0200, Peter Zijlstra wrote:
> > > On Tue, Jul 15, 2025 at 09:14:18AM +0200, Gabriele Monaco wrote:
> > > > Currently, the userspace RV tool skips trace events triggered by the RV
> > > > tool itself, this can be changed by passing the parameter -s, which
> > > > sets the variable config_my_pid to 0 (instead of the tool's PID). The
> > > > current condition for per-task monitors (config_has_id) does not check
> > > > that config_my_pid isn't 0 to skip. In case we pass -s, we show events
> > > > triggered by RV but don't show those triggered by idle (PID 0).
> > > 
> > > The distinction between !my_pid and has_id is that you can in fact trace
> > > pid-0 if you want?
> > > 
> > Yes pretty much, no flag is meant to skip events from pid-0.
> 
> > > > -	if (config_has_id && (config_my_pid == id))
> > > > +	if (config_my_pid && config_has_id && (config_my_pid == id))
> 
> But should we then not write:
> 
> 	if (config_has_id && (config_my_pid == id))

Sorry, got a bit confused, I flipped the two while describing:
* -s shows traces from RV but skips from pid-0 (unintended)
* omitting -s skips events from RV (correct)

If we are running a per-task monitor config_has_id is always true, we pass -s,
which makes config_my_pid = 0 (intended /not/ to skip RV).
Now when we are about to trace an event from idle (id=0), we skip it, although
we really shouldn't.
That's why we also needs to check for config_my_pid not being 0.

Does it make sense?

Thanks,
Gabriele