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Subject: Re: [PATCH 1/2] perf: Add persistent events
From: Peter Zijlstra <peterz@infradead.org>
To: Borislav Petkov <bp@alien8.de>
Cc: Ingo Molnar <mingo@elte.hu>, Frederic Weisbecker <fweisbec@gmail.com>,
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Date: Sun, 23 May 2010 21:23:21 +0200
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On Sun, 2010-05-23 at 20:54 +0200, Borislav Petkov wrote:
> From: Peter Zijlstra <peterz@infradead.org>
> Date: Sun, May 23, 2010 at 08:40:47PM +0200
> 
> > > > A persistent event would simply be a regular event, but created by the
> > > > kernel and not tied to a file-desc's lifetime.
> > > 
> > > So you're saying the trace_mce_record() tracepoint for example should
> > > be created completely internally in the kernel and cease to be a
> > > tracepoint? Will it still be able to be selected by perf -e?
> > 
> > No, it should be a regular tracepoint as far as tracepoints are
> > concerned.
> > 
> > But the only thing persistence should add is an instance of a
> > perf_event, it should not modify either the perf_event nor the
> > tracepoint code.
> 
> which means that subsystems which initialize earlier than perf (mce,
> for example) should have to be notified when perf is ready so that they
> could register a persistent event. How does that sound?

Either we add some notifier thing, or we simply add an explicit call in
the init sequence after the perf_event subsystem is running. I would
suggest we start with some explicit call, and take it from there.