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Subject: Re: [PATCH] tracing: Add task activate/deactivate tracepoints
From: Peter Zijlstra <peterz@infradead.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Frederic Weisbecker <fweisbec@gmail.com>,
       LKML <linux-kernel@vger.kernel.org>,
       Steven Rostedt <rostedt@goodmis.org>
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Date: Mon, 31 May 2010 10:54:59 +0200
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On Mon, 2010-05-31 at 10:12 +0200, Peter Zijlstra wrote:
> On Mon, 2010-05-31 at 10:00 +0200, Ingo Molnar wrote:
> > > 
> > > 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? 
> 
> Right, so a few of those corner cases I mentioned above are things like
> re-nice, PI-boosts etc.. Those use deactivate, modify task-state,
> activate cycles. so if you want to see those, we can add an explicit
> tracepoint for those actions.
> 
> An explicit nice/PI-boost tracepoint is much clearer than trying to
> figure out wth the deactivate/activate cycle was for.

Another advantage of explicit tracepoints is that you'd see them even
for non-running tasks, because we only do the deactivate/activate thingy
for runnable tasks.