[115/116] x86: Fix sched_clock_cpu for systems with unsynchronized TSC
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From: Greg KH on 30 Mar 2010 20:00 2.6.32-stable review patch. If anyone has any objections, please let us know. ------------------ From: Dimitri Sivanich <sivanich(a)sgi.com> commit 14be1f7454ea96ee614467a49cf018a1a383b189 upstream. On UV systems, the TSC is not synchronized across blades. The sched_clock_cpu() function is returning values that can go backwards (I've seen as much as 8 seconds) when switching between cpus. As each cpu comes up, early_init_intel() will currently set the sched_clock_stable flag true. When mark_tsc_unstable() runs, it clears the flag, but this only occurs once (the first time a cpu comes up whose TSC is not synchronized with cpu 0). After this, early_init_intel() will set the flag again as the next cpu comes up. Only set sched_clock_stable if tsc has not been marked unstable. Signed-off-by: Dimitri Sivanich <sivanich(a)sgi.com> Acked-by: Venkatesh Pallipadi <venkatesh.pallipadi(a)intel.com> Acked-by: Peter Zijlstra <a.p.zijlstra(a)chello.nl> LKML-Reference: <20100301174815.GC8224(a)sgi.com> Signed-off-by: Ingo Molnar <mingo(a)elte.hu> Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de> --- arch/x86/kernel/cpu/intel.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/arch/x86/kernel/cpu/intel.c +++ b/arch/x86/kernel/cpu/intel.c @@ -70,7 +70,8 @@ static void __cpuinit early_init_intel(s if (c->x86_power & (1 << 8)) { set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC); set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC); - sched_clock_stable = 1; + if (!check_tsc_unstable()) + sched_clock_stable = 1; } /* -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |