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

[Ingo Molnar <mingo@elte.hu>]

* Christoph Hellwig <hch@infradead.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@linux.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