linux-kernel - [patch] clocksource: add verification (watchdog) helper, fix

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Message-ID: <20070124154227.GA20726@elte.hu>
Date:	Wed, 24 Jan 2007 16:42:27 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Andrew Morton <akpm@...l.org>, LKML <linux-kernel@...r.kernel.org>,
	John Stultz <johnstul@...ibm.com>,
	Arjan van de Veen <arjan@...radead.org>,
	Roman Zippel <zippel@...ux-m68k.org>
Subject: [patch] clocksource: add verification (watchdog) helper, fix


one out of my 10 testsystems didnt properly enter high-res mode (but 
safely fell back to low-res mode), the patch below fixes this.

	Ingo

---------------------------->
Subject: [patch] clocksource: add verification (watchdog) helper, fix
From: Ingo Molnar <mingo@...e.hu>

if a clocksource is being verified by the watchdog, but the watchdog 
clocksource is registered /after/ the possibly-unstable clocksource has 
been registered, then when we switch that clocksource into high-res 
capable mode we also need to propagate this fact to the rest of the 
system - so that it properly switches into high-res mode.

this solves one particular system not entering high-res mode (but 
falling back to low-res mode) - with this patch it properly enters 
high-res mode:

 Switched to high resolution mode on CPU 0
 Switched to high resolution mode on CPU 1
 Switched to high resolution mode on CPU 2
 Switched to high resolution mode on CPU 3

Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/time/clocksource.c |   11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

Index: linux/kernel/time/clocksource.c
===================================================================
--- linux.orig/kernel/time/clocksource.c
+++ linux/kernel/time/clocksource.c
@@ -28,6 +28,7 @@
 #include <linux/sysdev.h>
 #include <linux/init.h>
 #include <linux/module.h>
+#include <linux/tick.h>
 
 /* XXX - Would like a better way for initializing curr_clocksource */
 extern struct clocksource clocksource_jiffies;
@@ -106,8 +107,16 @@ static void clocksource_watchdog(unsigne
 		/* Initialized ? */
 		if (!(cs->flags & CLOCK_SOURCE_WATCHDOG)) {
 			if ((cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
-			    (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS))
+			    (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
 				cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
+				/*
+				 * We just marked the clocksource as
+				 * highres-capable, notify the rest of the
+				 * system as well so that we transition
+				 * into high-res mode:
+				 */
+				tick_clock_notify();
+			}
 			cs->flags |= CLOCK_SOURCE_WATCHDOG;
 			cs->wd_last = csnow;
 		} else {
-
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