[PATCH] x86-64: Synchronize RDTSC on single core AMD

There is no guarantee that two RDTSCs in a row are monotonic,
so don't assume it on single core AMD systems.
This will make gettimeofday slower again
Signed-off-by: Andi Kleen <ak@suse.de>

1 files changed, 2 insertions, 5 deletions

diff --git a/arch/x86_64/kernel/setup.c b/arch/x86_64/kernel/setup.c
index a570c81c8316..05eaca41802b 100644
--- a/arch/x86_64/kernel/setup.c
+++ b/arch/x86_64/kernel/setup.c
@@ -732,11 +732,8 @@ static void __cpuinit init_amd(struct cpuinfo_x86 *c)
         /* Fix cpuid4 emulation for more */
         num_cache_leaves = 3;
 
-        /* When there is only one core no need to synchronize RDTSC */
-        if (num_possible_cpus() == 1)
-                set_bit(X86_FEATURE_SYNC_RDTSC, &c->x86_capability);
-        else
-                clear_bit(X86_FEATURE_SYNC_RDTSC, &c->x86_capability);
+        /* RDTSC can be speculated around */
+        clear_bit(X86_FEATURE_SYNC_RDTSC, &c->x86_capability);
 }
 
 static void __cpuinit detect_ht(struct cpuinfo_x86 *c)