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

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Message-ID: <1304558210.2943.24.camel@work-vm>
Date:	Wed, 04 May 2011 18:16:50 -0700
From:	john stultz <johnstul@...ibm.com>
To:	Christian Hoffmann <email@...istianhoffmann.info>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Long timeout when booting >= 2.6.38

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.

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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