[PATCH] x86: rewrite SMP TSC sync code
make the TSC synchronization code more robust, and unify it between x86_64 and
i386.
The biggest change is the removal of the 'fix up TSCs' code on x86_64 and
i386, in some rare cases it was /causing/ time-warps on SMP systems.
The new code only checks for TSC asynchronity - and if it can prove a
time-warp (if it can observe the TSC going backwards when going from one CPU
to another within a critical section), then the TSC clock-source is turned
off.
The TSC synchronization-checking code also got moved into a separate file.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/i386/kernel/tsc.c b/arch/i386/kernel/tsc.c
index 6f6971d..0fd9310 100644
--- a/arch/i386/kernel/tsc.c
+++ b/arch/i386/kernel/tsc.c
@@ -406,8 +406,10 @@
* Make an educated guess if the TSC is trustworthy and synchronized
* over all CPUs.
*/
-static __init int unsynchronized_tsc(void)
+__cpuinit int unsynchronized_tsc(void)
{
+ if (!cpu_has_tsc || tsc_unstable)
+ return 1;
/*
* Intel systems are normally all synchronized.
* Exceptions must mark TSC as unstable: