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Date: Sun, 18 Mar 2007 00:12:35 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: tglx@linutronix.de
Cc: Maxim Levitsky <maximlevitsky@gmail.com>, linux-kernel@vger.kernel.org,
       Ingo Molnar <mingo@elte.hu>, Adrian Bunk <bunk@stusta.de>,
       Arjan van de Ven <arjan@infradead.org>, Len Brown <lenb@kernel.org>
Subject: Re: [PATCH] i386: trust the PM-Timer calibration of the local APIC
 timer
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On Sat, 17 Mar 2007 01:04:56 +0100 Thomas Gleixner <tglx@linutronix.de> wrote:

> When PM-Timer is available for local APIC timer calibration we can skip
> the verification of the calibrated time value. The resulting error is
> quite small on a bunch of evaluated platforms and is less harming than
> the observed false positives.
> 
> We need to keep the verification on systems, which have no PM-Timer to
> avoid bogus local APIC timer calibrations in the range of factor 2-10,
> which can be observed when swicthing off the PM-timer support in the
> kernel configuration.
> 
> The wrong calibration values are probably caused by SMM code trying to
> emulate a PS/2 keyboard from a (maybe connected or not) USB keyboard.
> This prohibits the accurate delivery of PIT interrupts, which are used
> to calibrate the local APIC timer. Unfortunately we have no way to
> disable this BIOS misfeature in the early boot process.
> 
> Add also the dropped cpu_relax() back to the wait loops.

Is this a for-2.6.21 thing?