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Commit 14be1f74 authored by Dimitri Sivanich's avatar Dimitri Sivanich Committed by Ingo Molnar
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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: default avatarDimitri Sivanich <sivanich@sgi.com>
Acked-by: default avatarVenkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20100301174815.GC8224@sgi.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 13dda80e

arch/x86/kernel/cpu/intel.c

+2 −1
Original line number Diff line number Diff line
@@ -70,6 +70,7 @@ 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);

		if (!check_tsc_unstable())

			sched_clock_stable = 1;

	}