| From 14be1f7454ea96ee614467a49cf018a1a383b189 Mon Sep 17 00:00:00 2001 |
| From: Dimitri Sivanich <sivanich@sgi.com> |
| Date: Mon, 1 Mar 2010 11:48:15 -0600 |
| Subject: x86: Fix sched_clock_cpu for systems with unsynchronized TSC |
| |
| From: Dimitri Sivanich <sivanich@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@sgi.com> |
| Acked-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> |
| Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> |
| LKML-Reference: <20100301174815.GC8224@sgi.com> |
| Signed-off-by: Ingo Molnar <mingo@elte.hu> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@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; |
| } |
| |
| /* |
