linux-kernel - Re: Long timeout when booting >= 2.6.38

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Date:	Thu, 5 May 2011 10:25:46 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	john stultz <johnstul@...ibm.com>
cc:	Christian Hoffmann <email@...istianhoffmann.info>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Long timeout when booting >= 2.6.38

On Wed, 4 May 2011, john stultz wrote:

> On Wed, 2011-05-04 at 09:31 +0200, Christian Hoffmann wrote:
> > In fact, switching to acpi_pm doesn't seem to work:
> > 
> > $ dmesg | grep clock
> > 
> > [    0.000000] Command line: BOOT_IMAGE=/vmlinuz-2.6.39-rc5-ch-broken+ 
> > root=/dev/mapper/vg-root ro quiet splash vt.handoff=7 clocksource=acpi_pm
> > [    0.000000] Kernel command line: 
> > BOOT_IMAGE=/vmlinuz-2.6.39-rc5-ch-broken+ root=/dev/mapper/vg-root ro 
> > quiet splash vt.handoff=7 clocksource=acpi_pm
> > [    0.000000] hpet clockevent registered
> > [    1.413835] Switching to clocksource hpet
> > [    1.420762] Override clocksource acpi_pm is not HRT compatible. 
> > Cannot switch while in HRT/NOHZ mode
> > [  147.940143] Refined TSC clocksource calibration: 2809.409 MHz.
> > [  147.940147] Switching to clocksource tsc
> 
> So I think I've sorted this out.
> 
> The watchdog code is what enables CLOCK_SOURCE_VALID_FOR_HRES, but we
> actually end up selecting the clocksource before we enqueue it into the
> watchdog list, so that's why we see the warning.
> 
> I suspect the following will resolve this detail.

It does. Good catch!

> Signed-off-by: John Stultz <johnstul@...ibm.com>
> 
> diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
> index 6519cf6..0e17c10 100644
> --- a/kernel/time/clocksource.c
> +++ b/kernel/time/clocksource.c
> @@ -685,8 +685,8 @@ int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
>  	/* Add clocksource to the clcoksource list */
>  	mutex_lock(&clocksource_mutex);
>  	clocksource_enqueue(cs);
> -	clocksource_select();
>  	clocksource_enqueue_watchdog(cs);
> +	clocksource_select();
>  	mutex_unlock(&clocksource_mutex);
>  	return 0;
>  }
> @@ -706,8 +706,8 @@ int clocksource_register(struct clocksource *cs)
>  
>  	mutex_lock(&clocksource_mutex);
>  	clocksource_enqueue(cs);
> -	clocksource_select();
>  	clocksource_enqueue_watchdog(cs);
> +	clocksource_select();
>  	mutex_unlock(&clocksource_mutex);
>  	return 0;
>  }
> 
> 
> 
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