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

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:

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On Wed, 2025-07-16 at 13:50 +0200, Peter Zijlstra wrote:

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On Tue, Jul 15, 2025 at 09:14:18AM +0200, Gabriele Monaco wrote:

quoted

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.

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-	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