[PATCH] x86: Log reason why TSC was marked unstable

Change mark_tsc_unstable() so it takes a string argument, which holds the
reason the TSC was marked unstable.

This is then displayed the first time mark_tsc_unstable is called.

This should help us better debug why the TSC was marked unstable on certain
systems and allow us to make sure we're not being overly paranoid when
throwing out this troublesome clocksource.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andi Kleen <ak@suse.de>

2 files changed, 4 insertions, 3 deletions

diff --git a/arch/i386/kernel/cpu/cyrix.c b/arch/i386/kernel/cpu/cyrix.c
index f0badfdd4e45..e77f8e1cf7aa 100644
--- a/arch/i386/kernel/cpu/cyrix.c
+++ b/arch/i386/kernel/cpu/cyrix.c
@@ -279,7 +279,7 @@ static void __cpuinit init_cyrix(struct cpuinfo_x86 *c)
                  */  
                 if (vendor == PCI_VENDOR_ID_CYRIX &&
          (device == PCI_DEVICE_ID_CYRIX_5510 || device == PCI_DEVICE_ID_CYRIX_5520))
-                        mark_tsc_unstable();
+                        mark_tsc_unstable("cyrix 5510/5520 detected");
         }
 #endif
                 c->x86_cache_size=16;   /* Yep 16K integrated cache thats it */
diff --git a/arch/i386/kernel/tsc.c b/arch/i386/kernel/tsc.c
index 6cb8f5336732..755209dc93e1 100644
--- a/arch/i386/kernel/tsc.c
+++ b/arch/i386/kernel/tsc.c
@@ -233,7 +233,7 @@ time_cpufreq_notifier(struct notifier_block *nb, unsigned long val, void *data)
                                  * TSC based sched_clock turns
                                  * to junk w/ cpufreq
                                  */
-                                mark_tsc_unstable();
+                                mark_tsc_unstable("cpufreq changes");
                         }
                 }
         }
@@ -281,11 +281,12 @@ static struct clocksource clocksource_tsc = {
                                   CLOCK_SOURCE_MUST_VERIFY,
 };
 
-void mark_tsc_unstable(void)
+void mark_tsc_unstable(char *reason)
 {
         if (!tsc_unstable) {
                 tsc_unstable = 1;
                 tsc_enabled = 0;
+                printk("Marking TSC unstable due to: %s.\n", reason);
                 /* Can be called before registration */
                 if (clocksource_tsc.mult)
                         clocksource_change_rating(&clocksource_tsc, 0);