linux-kernel - Re: [tip:x86/tsc] x86: Improve TSC calibration using a delayed workqueue

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Date:	Tue, 11 Jan 2011 09:37:15 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
cc:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	andi@...stfloor.org, johnstul@...ibm.com, williams@...hat.com,
	schwidefsky@...ibm.com, mingo@...e.hu,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/tsc] x86: Improve TSC calibration using a delayed
 workqueue

On Tue, 11 Jan 2011, Kirill A. Shutemov wrote:

> On Tue, Jan 11, 2011 at 09:26:48AM +0100, Thomas Gleixner wrote:
> > On Tue, 11 Jan 2011, Kirill A. Shutemov wrote:
> > 
> > > On Sun, Dec 05, 2010 at 11:18:53AM +0000, tip-bot for John Stultz wrote:
> > > > Commit-ID:  08ec0c58fb8a05d3191d5cb6f5d6f81adb419798
> > > > Gitweb:     http://git.kernel.org/tip/08ec0c58fb8a05d3191d5cb6f5d6f81adb419798
> > > > Author:     John Stultz <johnstul@...ibm.com>
> > > > AuthorDate: Tue, 27 Jul 2010 17:00:00 -0700
> > > > Committer:  John Stultz <john.stultz@...aro.org>
> > > > CommitDate: Thu, 2 Dec 2010 16:48:37 -0800
> > > > 
> > > > x86: Improve TSC calibration using a delayed workqueue
> > > 
> > > This commit breaks booting the kernel in qemu with enabled KVM on my machine.
> > > .config attached.
> > > 
> > > [    0.424013] divide error: 0000 [#1] 
> > 
> > Got fixed by a8760ec (x86: Check tsc available/disabled in the delayed
> > init function)
> 
> No, it didn't. :(
> 
> I am able to reproduce it on current Linus' tree (v2.6.37-4700-g8adbf8d).

Does the patch below fix it ? We can end up with tsc_khz=0 there :(

Thanks,

	tglx
---
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 03d2ea8..6a7d726 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -959,7 +959,8 @@ static void tsc_refine_calibration_work(struct work_struct *work)
 					(unsigned long)tsc_khz % 1000);
 
 out:
-	clocksource_register_khz(&clocksource_tsc, tsc_khz);
+	if (tsc_khz)
+		clocksource_register_khz(&clocksource_tsc, tsc_khz);
 }
 
 
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