From: Dimitri Sivanich Date: Mon, 1 Mar 2010 17:48:15 +0000 (-0600) Subject: x86: Fix sched_clock_cpu for systems with unsynchronized TSC X-Git-Tag: v2.6.33.2~4 X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=39ec71179f7c02f2a9c1b37b1132f2d091a9cf1c;p=karo-tx-linux.git x86: Fix sched_clock_cpu for systems with unsynchronized TSC 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 Acked-by: Venkatesh Pallipadi Acked-by: Peter Zijlstra LKML-Reference: <20100301174815.GC8224@sgi.com> Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman --- diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c index 879666f4d871..7e1cca13af35 100644 --- a/arch/x86/kernel/cpu/intel.c +++ b/arch/x86/kernel/cpu/intel.c @@ -70,7 +70,8 @@ static void __cpuinit early_init_intel(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); - sched_clock_stable = 1; + if (!check_tsc_unstable()) + sched_clock_stable = 1; } /*