linux-kernel - Re: [PATCH 0/9] oprofile, perf, x86: introduce new functions to reserve perfctrs

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Date:	Thu, 11 Mar 2010 13:47:16 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Robert Richter <robert.richter@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	oprofile-list <oprofile-list@...ts.sourceforge.net>
Subject: Re: [PATCH 0/9] oprofile, perf, x86: introduce new functions to
 reserve perfctrs


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Thu, 2010-03-04 at 18:59 +0100, Peter Zijlstra wrote:
> > On Thu, 2010-03-04 at 16:22 +0100, Robert Richter wrote:
> > > This patch set improves the perfctr reservation code. New functions
> > > are available to reserve a counter by its index only. It is no longer
> > > necessary to allocate both msrs of a counter which also improves the
> > > code and makes it easier.
> > > 
> > > For oprofile a handler is implemented that returns an error now if a
> > > counter is already reserved by a different subsystem such as perf or
> > > watchdog. Before, oprofile silently ignored that counter. Finally the
> > > new reservation functions can be used to allocate special parts of the
> > > pmu such as IBS, which is necessary to use IBS with perf too.
> > > 
> > > The patches are available in the oprofile tree:
> > > 
> > >  git://git.kernel.org/pub/scm/linux/kernel/git/rric/oprofile.git core
> > > 
> > > If there are no objections, I suggest to merge it into the
> > > tip/perf/core too, maybe after pending patches went in. If there are
> > > already conflicts, I will do the merge for this.
> > 
> > Right, so cleaning up that reservation code is nice, but wouldn't it be
> > much nicer to simply do away with all that and make everything use the
> > (low level) perf code?
> 
> Alternatively, could we maybe further simplify this reservation into:
> 
> int  reserve_pmu(void);
> void release_pmu(void);
> 
> And not bother with anything finer grained.

Yeah, that looks quite a bit simpler.

It's all about making it easier to live with legacies anyway - all modern 
facilities will use perf events to access the PMU.

	Ingo
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