x86: Reenable TSC sync check at boot, even with NONSTOP_TSC

Commit 83ce4009 did the following change
If the TSC is constant and non-stop, also set it reliable.

But, there seems to be few systems that will end up with TSC warp across
sockets, depending on how the cpus come out of reset. Skipping TSC sync
test on such systems may result in time inconsistency later.

So, reenable TSC sync test even on constant and non-stop TSC systems.
Set, sched_clock_stable to 1 by default and reset it in
mark_tsc_unstable, if TSC sync fails.

This change still gives perf benefit mentioned in 83ce4009 for systems
where TSC is reliable.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Acked-by: Suresh Siddha <suresh.b.siddha@intel.com>
LKML-Reference: <20091217202702.GA18015@linux-os.sc.intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 9c31e8b09d2c2676c29f87a68442e56878d6bece..879666f4d871c99a312169bd30aad71049713572 100644 (file)
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -70,7 +70,6 @@ static void __cpuinit early_init_intel(struct cpuinfo_x86 *c)
        if (c->x86_power & (1 << 8)) {
                set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
                set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC);
-               set_cpu_cap(c, X86_FEATURE_TSC_RELIABLE);
                sched_clock_stable = 1;
        }
 

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index cd982f48e23e11c74acd08e8db823c3ef4fe5886..597683aa5ba0ba3ef800ab39179669ded4e3aa57 100644 (file)
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -763,6 +763,7 @@ void mark_tsc_unstable(char *reason)
 {
        if (!tsc_unstable) {
                tsc_unstable = 1;
+               sched_clock_stable = 0;
                printk(KERN_INFO "Marking TSC unstable due to %s\n", reason);
                /* Change only the rating, when not registered */
                if (clocksource_tsc.mult)