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

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Message-ID: <48889C14.4070408@fujitsu-siemens.com>
Date:	Thu, 24 Jul 2008 17:13:24 +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

Hi Cyrill,

 > btw, Martin, don't get me wrong please - i'm not just complaining :)
 > The changes you propose is important enough _but_ it could introduce
 > regression. Look, with situation of miscalibrated apic timer kernel
 > was working before but with the patch it could stop to work. So if
 > user has a such screwed motherboard he could be shocked if it stop
 > booting with message about SMI happened. we defenitely have to provide
 > some workaround for this. And your max iteration counter solution
 > would be fine I think.

Let's see what other people think about this. I am fine with both 
solutions. Currently only the first one has been tested though (testing 
these patches thoroughly needs long-time reboot tests).

One more remark: There are similar calibration routines around in the 
kernel which suffer from similar problems as calibrate_APIC_clock(). 
AFAIK, only calibrate_delay() was made SMI-safe by Venkatesh Pallipadi 
years ago.

Martin

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Martin Wilck
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FSC IP ESP DEV 6

Fujitsu Siemens Computers GmbH
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