Messages in this thread | | | Subject | Re: [PATCH v2] x86: Fix sched_clock_cpu for systems with unsynchronized TSC | From | "Pallipadi, Venkatesh" <> | Date | Mon, 01 Mar 2010 09:58:00 -0800 |
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Acked-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
On Mon, 2010-03-01 at 09:48 -0800, Dimitri Sivanich wrote: > 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@sgi.com> > > --- > > Only affects x86 arch. > > arch/x86/kernel/cpu/intel.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > Index: linux/arch/x86/kernel/cpu/intel.c > =================================================================== > --- linux.orig/arch/x86/kernel/cpu/intel.c > +++ linux/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; > } > > /*
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