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Subject[PATCH] Fix sched_clock_cpu for systems with unsynchronized TSC
On UV systems, the TSC is not synchronized across blades.  The
sched_clock_cpu() function is returning values that can go backwards
(I've seen as much as 8 seconds) when switching between cpus.

As each cpu comes up, early_init_intel() will currently set the
sched_clock_stable flag true. When mark_tsc_unstable() runs, it clears
the flag, but this only occurs once (the first time a cpu comes up whose
TSC is not synchronized with cpu 0). After this, early_init_intel() will
set the flag again as the next cpu comes up.

This patch changes the logic to assume that the sched_clock is stable at
first. From then on it is only cleared.

Signed-off-by: Dimitri Sivanich <sivanich@sgi.com>

---

arch/x86/kernel/cpu/intel.c | 4 ++--
kernel/sched_clock.c | 2 +-
2 files changed, 3 insertions(+), 3 deletions(-)

Index: linux/arch/x86/kernel/cpu/intel.c
===================================================================
--- linux.orig/arch/x86/kernel/cpu/intel.c
+++ linux/arch/x86/kernel/cpu/intel.c
@@ -70,8 +70,8 @@ static void __cpuinit early_init_intel(s
if (c->x86_power & (1 << 8)) {
set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC);
- sched_clock_stable = 1;
- }
+ } else
+ sched_clock_stable = 0;

/*
* There is a known erratum on Pentium III and Core Solo
Index: linux/kernel/sched_clock.c
===================================================================
--- linux.orig/kernel/sched_clock.c
+++ linux/kernel/sched_clock.c
@@ -45,7 +45,7 @@ unsigned long long __attribute__((weak))
static __read_mostly int sched_clock_running;

#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
-__read_mostly int sched_clock_stable;
+__read_mostly int sched_clock_stable = 1;

struct sched_clock_data {
u64 tick_raw;

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