lkml.org 
[lkml]   [2010]   [Mar]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH v2] x86: Fix sched_clock_cpu for systems with unsynchronized TSC
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;
}

/*

\
 
 \ /
  Last update: 2010-03-01 18:51    [W:3.639 / U:0.564 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site