AcoSail/kernel_optimize_test
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[PATCH] x86_64: Don't try to synchronize the TSC over CPUs on Intel CPUs at boot.

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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>
This commit is contained in:
Andi Kleen 2006-01-11 22:45:15 +01:00 committed by Linus Torvalds
parent 3c02175113
commit 737c5c3bde
3 changed files with 11 additions and 3 deletions
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8
arch/x86_64/kernel/smpboot.c
View File

@ -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);
}

4
arch/x86_64/kernel/time.c
View File

@ -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;
}
/*

2
include/asm-x86_64/proto.h
View File

@ -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 *);