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

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Date:	Sat, 26 Jul 2008 17:40:29 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Martin Wilck <martin.wilck@...itsu-siemens.com>
Cc:	Cyrill Gorcunov <gorcunov@...il.com>,
	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 3)


* Martin Wilck <martin.wilck@...itsu-siemens.com> wrote:

> [PATCH] x86 (64): make calibrate_APIC_clock() SMI-safe (take 3)
> 
> Non-maskable asynchronous events (e.g. SMIs) which occur during the 
> APIC timer calibration can cause timer miscalibrations, sometimes by 
> large amounts. This patch fixes this by making sure that no 
> significant interruption occurs between APIC and TSC reads. SMIs may 
> still occur at some stage in the calibration loop, causing the loop to 
> last longer than intended. This doesn't matter though, as long as the 
> start and end values are both taken simultaneously.
> 
> Changed wrt take 2: Use max. possible start value for the APIC timer 
> to avoid underflow.
> 
> Signed-off-by: Martin Wilck <martin.wilck@...itsu-siemens.com>
> Signed-off-by: Gerhard Wichert <gerhard.wichert@...itsu-siemens.com>
> 
> --- arch/x86/kernel/apic_64.c	2008-07-25 15:39:51.000000000 +0200
> +++ arch/x86/kernel/apic_64.c.new	2008-07-25 15:55:08.000000000 +0200

nice - could you please implement it symmetrically on 32-bit APIC 
calibration as well?

	Ingo
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