[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>
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@ -335,7 +335,13 @@ static __cpuinit void sync_tsc(unsigned int master)
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static void __cpuinit tsc_sync_wait(void)
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static void __cpuinit tsc_sync_wait(void)
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{
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{
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if (notscsync || !cpu_has_tsc)
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/*
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* When the CPU has synchronized TSCs assume the BIOS
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* or the hardware already synced. Otherwise we could
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* mess up a possible perfect synchronization with a
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* not-quite-perfect algorithm.
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*/
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if (notscsync || !cpu_has_tsc || !unsynchronized_tsc())
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return;
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return;
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sync_tsc(0);
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sync_tsc(0);
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}
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}
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@ -953,7 +953,7 @@ void __init time_init(void)
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* Make an educated guess if the TSC is trustworthy and synchronized
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* Make an educated guess if the TSC is trustworthy and synchronized
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* over all CPUs.
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* over all CPUs.
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*/
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*/
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static __init int unsynchronized_tsc(void)
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__init int unsynchronized_tsc(void)
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{
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{
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#ifdef CONFIG_SMP
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#ifdef CONFIG_SMP
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if (oem_force_hpet_timer())
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if (oem_force_hpet_timer())
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@ -964,7 +964,7 @@ static __init int unsynchronized_tsc(void)
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return 0;
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return 0;
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#endif
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#endif
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/* Assume multi socket systems are not synchronized */
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/* Assume multi socket systems are not synchronized */
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return num_online_cpus() > 1;
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return num_present_cpus() > 1;
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}
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}
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/*
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/*
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@ -89,6 +89,8 @@ extern void check_efer(void);
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extern int unhandled_signal(struct task_struct *tsk, int sig);
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extern int unhandled_signal(struct task_struct *tsk, int sig);
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extern int unsynchronized_tsc(void);
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extern void select_idle_routine(const struct cpuinfo_x86 *c);
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extern void select_idle_routine(const struct cpuinfo_x86 *c);
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extern void gart_parse_options(char *);
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extern void gart_parse_options(char *);
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