linux-kernel - Re: [PATCH v2 02/14] perf: Add persistent events

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Message-ID: <20130625084600.GB21579@rric.localhost>
Date:	Tue, 25 Jun 2013 10:46:00 +0200
From:	Robert Richter <rric@...nel.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org,
	Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH v2 02/14] perf: Add persistent events

On 24.06.13 21:24:04, Borislav Petkov wrote:
> On Mon, Jun 24, 2013 at 11:28:07AM +0200, Peter Zijlstra wrote:
> > I find this patch incomplete for its asymmetric; there a dec, but not an
> > implied inc.
> 
> There's one in perf_mmap_open.
> 
> Basically the idea was to pull up the ->mmap_count decrement (haha,
> sounds like excrement :-)) and not deallocate the ring buffers for a
> persistent event.

The asymmetry comes from rb_alloc() in add_persistent_event_on_cpu()
which is usually implemented in the mmap functions. We might better
improve functions to attach/detach events and buffers for more
symmetric code.

-Robert
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