[PATCH] x86_64: Don't try to synchronize the TSC over CPUs on Intel CPUs at boot.
They already do this in hardware and the Linux algorithm
actually adds errors.
Cc: mingo@elte.hu
Cc: rohit.seth@intel.com
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/arch/x86_64/kernel/smpboot.c b/arch/x86_64/kernel/smpboot.c
index e6af93b..9947285 100644
--- a/arch/x86_64/kernel/smpboot.c
+++ b/arch/x86_64/kernel/smpboot.c
@@ -335,7 +335,13 @@
static void __cpuinit tsc_sync_wait(void)
{
- if (notscsync || !cpu_has_tsc)
+ /*
+ * When the CPU has synchronized TSCs assume the BIOS
+ * or the hardware already synced. Otherwise we could
+ * mess up a possible perfect synchronization with a
+ * not-quite-perfect algorithm.
+ */
+ if (notscsync || !cpu_has_tsc || !unsynchronized_tsc())
return;
sync_tsc(0);
}
diff --git a/arch/x86_64/kernel/time.c b/arch/x86_64/kernel/time.c
index 211bf0e..f8d4b69 100644
--- a/arch/x86_64/kernel/time.c
+++ b/arch/x86_64/kernel/time.c
@@ -953,7 +953,7 @@
* Make an educated guess if the TSC is trustworthy and synchronized
* over all CPUs.
*/
-static __init int unsynchronized_tsc(void)
+__init int unsynchronized_tsc(void)
{
#ifdef CONFIG_SMP
if (oem_force_hpet_timer())
@@ -964,7 +964,7 @@
return 0;
#endif
/* Assume multi socket systems are not synchronized */
- return num_online_cpus() > 1;
+ return num_present_cpus() > 1;
}
/*
diff --git a/include/asm-x86_64/proto.h b/include/asm-x86_64/proto.h
index 56dc70b..115e496 100644
--- a/include/asm-x86_64/proto.h
+++ b/include/asm-x86_64/proto.h
@@ -89,6 +89,8 @@
extern int unhandled_signal(struct task_struct *tsk, int sig);
+extern int unsynchronized_tsc(void);
+
extern void select_idle_routine(const struct cpuinfo_x86 *c);
extern void gart_parse_options(char *);
