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

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Date:	Thu, 1 Oct 2009 09:25:18 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	prasad@...ux.vnet.ibm.com, "Frank Ch. Eigler" <fche@...hat.com>,
	peterz@...radead.org, linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [RFC PATCH] perf_core: provide a kernel-internal interface to
	get to performance counters


* Arjan van de Ven <arjan@...radead.org> wrote:

> On Sun, 27 Sep 2009 00:02:46 +0530
> "K.Prasad" <prasad@...ux.vnet.ibm.com> wrote:
> 
> > On Sat, Sep 26, 2009 at 12:03:28PM -0400, Frank Ch. Eigler wrote:
> 
> > > For what it's worth, this sort of thing also looks useful from 
> > > systemtap's point of view.
> > 
> > Wouldn't SystemTap be another user that desires support for 
> > multiple/all CPU perf-counters (apart from hw-breakpoints as a 
> > potential user)? As Arjan pointed out, perf's present design would 
> > support only a per-CPU or per-task counter; not both.
> 
> I'm sorry but I think I am missing your point. "all cpu counters" 
> would be one small helper wrapper away, a helper I'm sure the 
> SystemTap people are happy to submit as part of their patch series 
> when they submit SystemTap to the kernel.

Yes, and Frederic wrote that wrapper already for the hw-breakpoints 
patches. It's a non-issue and does not affect the design - we can always 
gang up an array of per cpu perf events, it's a straightforward use of 
the existing design.

User-space tools have been doing this for ages already, 'perf top' will 
open an array of per cpu events to monitor all events in the system.

	Ingo
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