[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 (file)
--- a/arch/x86_64/kernel/smpboot.c
+++ b/arch/x86_64/kernel/smpboot.c
@@ -335,7 +335,13 @@ static __cpuinit void sync_tsc(unsigned int master)
 
 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 (file)
--- a/arch/x86_64/kernel/time.c
+++ b/arch/x86_64/kernel/time.c
@@ -953,7 +953,7 @@ void __init time_init(void)
  * 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 @@ static __init int unsynchronized_tsc(void)
                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 (file)
--- a/include/asm-x86_64/proto.h
+++ b/include/asm-x86_64/proto.h
@@ -89,6 +89,8 @@ extern void check_efer(void);
 
 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 *);