[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>

3 files changed, 5 insertions, 4 deletions

diff --git a/arch/x86_64/kernel/time.c b/arch/x86_64/kernel/time.c
index 5f862e216a42..91c9066a380d 100644
--- a/arch/x86_64/kernel/time.c
+++ b/arch/x86_64/kernel/time.c
@@ -397,7 +397,7 @@ void __init time_init(void)
                 cpu_khz = tsc_calibrate_cpu_khz();
 
         if (unsynchronized_tsc())
-                mark_tsc_unstable();
+                mark_tsc_unstable("TSCs unsynchronized");
 
         if (cpu_has(&boot_cpu_data, X86_FEATURE_RDTSCP))
                 vgetcpu_mode = VGETCPU_RDTSCP;
diff --git a/arch/x86_64/kernel/tsc.c b/arch/x86_64/kernel/tsc.c
index 5c84992c676d..48f9a8e6aa91 100644
--- a/arch/x86_64/kernel/tsc.c
+++ b/arch/x86_64/kernel/tsc.c
@@ -111,7 +111,7 @@ static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
 
                 tsc_khz = cpufreq_scale(tsc_khz_ref, ref_freq, freq->new);
                 if (!(freq->flags & CPUFREQ_CONST_LOOPS))
-                        mark_tsc_unstable();
+                        mark_tsc_unstable("cpufreq changes");
         }
 
         set_cyc2ns_scale(tsc_khz_ref);
@@ -199,10 +199,11 @@ static struct clocksource clocksource_tsc = {
         .vread                  = vread_tsc,
 };
 
-void mark_tsc_unstable(void)
+void mark_tsc_unstable(char *reason)
 {
         if (!tsc_unstable) {
                 tsc_unstable = 1;
+                printk("Marking TSC unstable due to %s\n", reason);
                 /* Change only the rating, when not registered */
                 if (clocksource_tsc.mult)
                         clocksource_change_rating(&clocksource_tsc, 0);
diff --git a/arch/x86_64/kernel/tsc_sync.c b/arch/x86_64/kernel/tsc_sync.c
index 72d444dede9b..355f5f506c81 100644
--- a/arch/x86_64/kernel/tsc_sync.c
+++ b/arch/x86_64/kernel/tsc_sync.c
@@ -138,7 +138,7 @@ void __cpuinit check_tsc_sync_source(int cpu)
                 printk("\n");
                 printk(KERN_WARNING "Measured %Ld cycles TSC warp between CPUs,"
                                     " turning off TSC clock.\n", max_warp);
-                mark_tsc_unstable();
+                mark_tsc_unstable("check_tsc_sync_source failed");
                 nr_warps = 0;
                 max_warp = 0;
                 last_tsc = 0;