linux-kernel - Re: [RFC PATCH] perf_core: provide a kernel-internal interface to get to performance counters

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Message-ID: <20100207170156.GB25893@elte.hu>
Date:	Sun, 7 Feb 2010 18:01:56 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org, peterz@...radead.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	john smith <whalajam@...oo.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Don Zickus <dzickus@...hat.com>
Subject: Re: [RFC PATCH] perf_core: provide a kernel-internal interface to
 get to performance counters


* Christoph Hellwig <hch@...radead.org> wrote:

> On Fri, Sep 25, 2009 at 12:25:56PM +0200, Arjan van de Ven wrote:
> > >From 5db5cd76f3c16c9f6093f54d1ccfb97d04b9a1ca Mon Sep 17 00:00:00 2001
> > From: Arjan van de Ven <arjan@...ux.intel.com>
> > Date: Fri, 25 Sep 2009 12:20:57 +0200
> > Subject: [PATCH] perf_core: provide a kernel-internal interface to get to performance counters
> 
> So this patch got accepted into mainline a while ago, without a user ever 
> beeing presented, nevermind actually included in mainline.  Time to revert 
> providing these useless exports and dead code?

You are quite wrong about that, this API is being relied on by the upstream 
hw-breakpoints subsystem:

  earth4:~/tip> git grep perf_event_release_kernel
  include/linux/perf_event.h:extern int perf_event_release_kernel(struct perf_event *event);
  kernel/hw_breakpoint.c: perf_event_release_kernel(bp);
  [...]

Furthermore beyond the use mentioned by Arjan there's a new patch-set posted 
to LKML that makes use of this new API as well: the generalized NMI watchdog 
feature posted by Don Zickus.

Thanks,

	Ingo
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