linux-kernel - Re: [PATCH 1/2] perf: Add persistent events

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Date:	Fri, 28 May 2010 20:07:10 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Borislav Petkov <bp@...64.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Borislav Petkov <bp@...en8.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Lin Ming <ming.m.lin@...el.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] perf: Add persistent events

On Fri, 2010-05-28 at 17:57 +0200, Borislav Petkov wrote:
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Fri, May 28, 2010 at 05:17:40PM +0200
> 
> > On Fri, 2010-05-28 at 16:33 +0200, Ingo Molnar wrote:
> > 
> > > >  2) get these things a buffer, perf_events as created don't actually
> > > >     have an output buffer, normally that is created at mmap() time, but
> > > >     since you cannot mmap() a kernel side event, it doesn't get to have
> > > >     a buffer. This could be done by extracting perf_mmap_data_alloc()
> > > >     into a sensible interface.
> > > 
> > > #2 could be a new syscall: sys_create_ring_buffer or so?
> > 
> > No, they need a buffer in-kernel, syscalls aren't the ideal tool for
> > that :-)
> 
> Yeah, I need a per-cpu buffer ready at event registration/enable time,
> maybe even have perf_event_create_kernel_counter() take care of that
> buffer allocation with a flag or similar prior to enabling the event...
> 
> > I've got patches refactoring the whole buffer stuff to make it more a
> > self-contained entity.
> 
> Can I see those when you're done so that I can base my stuff on top?


They can be found at:

http://programming.kicks-ass.net/sekrit/patches.tar.bz2

ignore the last 5 patches, those are random hackery.

In particular, look at:

patches/perf-fix-buffer-redirect.patch
patches/perf-buffer.patch
patches/perf-buffer-init.patch

(they won't apply separately in that order, simply push the full queue
until the last one or further)

After that you should be able to add:

  buffer = perf_buffer_alloc(nr_pages, watermark, cpu, flags);
  rcu_assign_pointer(event->buffer, buffer);

to allocate and attach a buffer to your event (do so for each cpu's MCE
event).

After that we still need a way to expose all that to userspace, but at
least the events will be complete and able to record bits ;-)



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