linux-kernel - Re: [RFC PATCH 0/4] perf: Correlating user process data to samples

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Date: Fri, 12 Apr 2024 09:12:45 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Beau Belgrave <beaub@...ux.microsoft.com>
Cc: mingo@...hat.com, acme@...nel.org, namhyung@...nel.org,
	rostedt@...dmis.org, mhiramat@...nel.org,
	mathieu.desnoyers@...icios.com, linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org, mark.rutland@....com,
	alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
	irogers@...gle.com, adrian.hunter@...el.com, primiano@...gle.com,
	aahringo@...hat.com, dcook@...ux.microsoft.com
Subject: Re: [RFC PATCH 0/4] perf: Correlating user process data to samples

On Fri, Apr 12, 2024 at 12:17:28AM +0000, Beau Belgrave wrote:

> An idea flow would look like this:
> User Task		Profile
> do_work();		sample() -> IP + No activity
> ...
> set_activity(123);
> ...
> do_work();		sample() -> IP + activity (123)
> ...
> set_activity(124);
> ...
> do_work();		sample() -> IP + activity (124)

This, start with this, because until I saw this, I was utterly confused
as to what the heck you were on about.

I started by thinking we already have TID in samples so you can already
associate back to user processes and got increasingly confused the
further I went.

What you seem to want to do however is have some task-state included so
you can see what the thread is doing.

Anyway, since we typically run stuff from NMI context, accessing user
data is 'interesting'. As such I would really like to make this work
depend on the call-graph rework that pushes all the user access bits
into return-to-user.