linux-kernel - Re: [patch] x86, tsc: fix SMI induced variation in quick_pit

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Date:	Mon, 16 Jan 2012 18:47:36 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	asit.k.mallick@...el.com
Subject: Re: [patch] x86, tsc: fix SMI induced variation in quick_pit_calibrate()

On Mon, Jan 16, 2012 at 12:15 PM, Suresh Siddha
<suresh.b.siddha@...el.com> wrote:
> Linus, We are seeing NTP failures on a big cluster as a result of big
> variation in calibrated TSC values. Our debug showed that it is indeed
> because of the SMI and its effect on quick pit calibration. Appended
> patch helps fix it. It ran over the weekend boot tests with out any
> failures.
>
>
>  [ As far as the SMI source is concerned, this is a periodic SMI that gets
>    disabled after ACPI is enabled by the OS. But the TSC calibration happens
>    before the ACPI is enabled. ]
>

Hi, Suresh

Do you know what is SMI doing at that time ? with USB legacy emulating?

I have some patches that will do USB hand off early.
Wonder if that would help.
please check those patches at

git://git.kernel.org/pub/scm/linux/kernel/git/yinghai/linux-yinghai.git
usb_smi_disable_early

Thanks

Yinghai Lu
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