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

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Date:	Tue, 11 Jan 2011 11:56:40 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Thomas Gleixner <tglx@...utronix.de>
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, Jan 11, 2011 at 09:37:15AM +0100, Thomas Gleixner wrote:
> 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 :(

Yes, it does.

Bisected-and-tested-by: Kirill A. Shutemov <kas@...nvz.org>

Thanks.

> 
> 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);
>  }
>  
>  

-- 
 Kirill A. Shutemov
--
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