[PATCH] Don't synchronize time reading on single core AMD systems

We do some additional CPU synchronization in gettimeofday et.al. to make
sure the time stamps are always monotonic over multiple CPUs. But on
single core systems that is not needed. So don't do it.
Signed-off-by: Andi Kleen <ak@suse.de>

arch/x86_64/kernel/setup.c

@@ -728,6 +728,12 @@ 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);
 }
 
 static void __cpuinit detect_ht(struct cpuinfo_x86 *c)