linux-kernel - Re: [PATCH 1/2] Separate the performance counter allocation from the LAPIC NMI watchdog

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Message-ID: <20070620131829.GA17256@atjola.homenet>
Date:	Wed, 20 Jun 2007 15:18:29 +0200
From:	Björn Steinbrink <B.Steinbrink@....de>
To:	Andi Kleen <ak@...e.de>
Cc:	eranian@....hp.com, oprofile-list@...ts.sourceforge.net,
	wcohen@...hat.com, perfmon@...ali.hpl.hp.com,
	linux-kernel@...r.kernel.org, levon@...ementarian.org,
	akpm@...ux-foundation.org, mingo@...e.hu
Subject: Re: [PATCH 1/2] Separate the performance counter allocation from the LAPIC NMI watchdog

On 2007.06.20 14:31:43 +0200, Andi Kleen wrote:
> On Wednesday 20 June 2007 12:35:56 Björn Steinbrink wrote:
> > The performance counter allocator is tied to the LAPIC NMI watchdog,
> 
> That's not true. It's completely independent. It just happens to be in
> the same file, but it has no direct functional ties to the watchdog.

The allocator relies on the wd_ops structure, which is only initialized
if the LAPIC NMI watchdog is enabled. If it is not enabled, the
functions that convert from absolute perfctr/evntsel addresses to
offsets from the respective base address break, and always return 0.

> > Fix the performance counter allocator by making it independent of the
> > LAPIC NMI watchdog. This also fixes a bug in the LAPIC NMI watchdog
> > which allocated the wrong performance counter on CPUs with PerfMon
> > support.
> 
> Combining code movement with functional fixes makes it impossible
> to review properly. Don't do that please.

Ok.

Björn
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