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Date: Fri, 12 Apr 2024 09:12:45 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Beau Belgrave <beaub@linux.microsoft.com>
Cc: mingo@redhat.com, acme@kernel.org, namhyung@kernel.org,
	rostedt@goodmis.org, mhiramat@kernel.org,
	mathieu.desnoyers@efficios.com, linux-kernel@vger.kernel.org,
	linux-trace-kernel@vger.kernel.org,
	linux-perf-users@vger.kernel.org, mark.rutland@arm.com,
	alexander.shishkin@linux.intel.com, jolsa@kernel.org,
	irogers@google.com, adrian.hunter@intel.com, primiano@google.com,
	aahringo@redhat.com, dcook@linux.microsoft.com
Subject: Re: [RFC PATCH 0/4] perf: Correlating user process data to samples
Message-ID: <20240412071245.GD30852@noisy.programming.kicks-ass.net>
References: <20240412001732.475-1-beaub@linux.microsoft.com>
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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.