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Date: Fri, 25 Jul 2008 18:15:02 +0400 From: Cyrill Gorcunov <gorcunov@...il.com> To: Martin Wilck <martin.wilck@...itsu-siemens.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 3) [Martin Wilck - Fri, Jul 25, 2008 at 04:01:08PM +0200] > Cyrill Gorcunov wrote: > >> Martin, if I understood you right - this means your patch is not >> needed? > > The patch would still be needed. Just the reported failure of my > simplified patch on the old kernel would not have occurred in the > current kernel. IOW, the patch is fine for the current kernel, but not > for the old one. > >> Actually on 64bit mode APIC_DIVISOR is a bit hidden in >> __setup_APIC_LVTT - you may see it as APIC_TDR_DIV_16 while setting >> up divisor register. I was proposing patch for that but it leaded >> to potetntial overflow (thanks Ingo for catching) so we leave it as >> is. Maybe I miss something? > > The problem was not that the divisor 16 was used for the counter speed > (APIC_TDR_DIV_16), but that the old code set the counter start value to > (250000000/16) rather than just 250000000. That means the counter will > underflow earlier. > > I am attaching a "take 3" patch which minimizes the risk of an underflow > by using the maximum possible initial value for the APIC timer. > > Martin > > -- > Martin Wilck > PRIMERGY System Software Engineer > FSC IP ESP DEV 6 > > Fujitsu Siemens Computers GmbH > Heinz-Nixdorf-Ring 1 > 33106 Paderborn > Germany > > Tel: ++49 5251 8 15113 > Fax: ++49 5251 8 20209 > Email: mailto:martin.wilck@...itsu-siemens.com > Internet: http://www.fujitsu-siemens.com > Company Details: http://www.fujitsu-siemens.com/imprint.html > ah, ok, thanks - Cyrill - -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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