linux-kernel - Re: [PATCH] tracing: Add task activate/deactivate tracepoints

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Message-ID: <20100531080049.GA435@elte.hu>
Date:	Mon, 31 May 2010 10:00:49 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] tracing: Add task activate/deactivate tracepoints


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Fri, 2010-05-28 at 16:26 +0200, Frederic Weisbecker wrote:
> > We have various tracepoints that tell us when a task is going to
> > be enqueued in a runqueue: fork, wakeup, migrate.
> > 
> > But they don't always provide us the level of information necessary
> > to know what is actually in which runqueue, precisely because the
> > migrate event is only fired if the task is queued on another
> > cpu than its previous one. So we don't always know where a waking up
> > task goes.
> > 
> > And moreover we don't have events that tells a task goes to sleep,
> > and even that wouldn't cover every cases when a task is dequeued.
> > 
> > So bring these two new tracepoints to get informations about the
> > load of each runqueues.
> 
> NAK, aside from a few corner cases wakeup and sleep are the important 
> points.
> 
> The activate and deactivate functions are implementation details.

Frederic, can you show us a concrete example of where we dont know what is 
going on due to inadequate instrumentation? Can we fix that be extending the 
existing tracepoints?

	Ingo
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