From c98fdeaa92731308ed80386261fa2589addefa47 Mon Sep 17 00:00:00 2001 From: Borislav Petkov Date: Tue, 7 Feb 2012 13:08:52 +0100 Subject: [PATCH] x86/sched/perf/AMD: Set sched_clock_stable Stephane Eranian reported that doing a scheduler latency measurements with perf on AMD doesn't work out as expected due to the fact that the sched_clock() granularity is too coarse, i.e. done in jiffies due to the sched_clock_stable not set, which, if set, would mean that we get to use the TSC as sample source which would give us much higher precision. However, there's no reason not to set sched_clock_stable on AMD because all families from F10h and upwards do have an invariant TSC and have the CPUID flag to prove (CPUID_8000_0007_EDX[8]). Make it so, #1. Signed-off-by: Borislav Petkov Cc: Borislav Petkov Cc: Venki Pallipadi Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Arnaldo Carvalho de Melo Cc: Robert Richter Cc: Eric Dumazet Cc: Andreas Herrmann Link: http://lkml.kernel.org/r/20120206132546.GA30854@quad [ Should any non-standard system break the TSC, we should mark them so explicitly, in their platform init handler, or in a DMI quirk. ] Signed-off-by: Ingo Molnar --- arch/x86/kernel/cpu/amd.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index f4773f4..0a44b90 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -5,6 +5,7 @@ #include #include +#include #include #include #include @@ -456,6 +457,8 @@ static void __cpuinit early_init_amd(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); + if (!check_tsc_unstable()) + sched_clock_stable = 1; } #ifdef CONFIG_X86_64 -- 2.7.4