From: Andi Kleen Date: Tue, 26 Sep 2006 08:52:41 +0000 (+0200) Subject: [PATCH] Don't synchronize time reading on single core AMD systems X-Git-Tag: v2.6.19-rc1~1077^2~15 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2049336f60d297c85ac977245b9326ec00396114;p=linux-2.6 [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 --- diff --git a/arch/x86_64/kernel/setup.c b/arch/x86_64/kernel/setup.c index 085f2e09b9..26524ce3b2 100644 --- a/arch/x86_64/kernel/setup.c +++ b/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)