linux-kernel - Re: [PATCH] x86 (64): make calibrate_APIC

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Message-ID: <4889D767.5050709@fujitsu-siemens.com>
Date:	Fri, 25 Jul 2008 15:38:47 +0200
From:	Martin Wilck <martin.wilck@...itsu-siemens.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Wichert, Gerhard" <Gerhard.Wichert@...itsu-siemens.com>,
	"Maciej W. Rozycki" <macro@...ux-mips.org>
Subject: Re: [PATCH] x86 (64): make calibrate_APIC_clock() SMI-safe (take
 2)

I wrote:

> I have to say that my simplified patch failed to do the calibration
> correctly on our test system (the original patch worked well). Please
> stay tuned, we are investigating this currently.

Please forget that. It was observed on an old "enterprise" kernel with 
which we are currently testing the backported patch with, and it was due 
to the fact that the initial counter value on that kernel was divided by 
APIC_DIVISOR (=16). The resulting initial counter value was too low in a 
"SMI flood" case, the counter could overlap. APIC_DIVISOR is no longer 
used in the current kernel.

Martin

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Martin Wilck
PRIMERGY System Software Engineer
FSC IP ESP DEV 6

Fujitsu Siemens Computers GmbH
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Germany

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