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x86: Implement support to synchronize RDTSC with LFENCE on Intel CPUs

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According to Intel RDTSC can be always synchronized with LFENCE
on all current CPUs. Implement the necessary CPUID bit for that.

It is unclear yet if that is true for all future CPUs too,
but if there's another way the kernel can be always updated.

Cc: asit.k.mallick@intel.com
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Andi Kleen 2008-01-30 13:32:37 +01:00 committed by Ingo Molnar
parent de4218634e
commit 707fa8ed92
3 changed files with 4 additions and 5 deletions
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3
arch/x86/kernel/cpu/intel.c
View file

@ -203,9 +203,10 @@ static void __cpuinit init_intel(struct cpuinfo_x86 *c)
}
#endif
if (cpu_has_xmm)
set_bit(X86_FEATURE_LFENCE_RDTSC, c->x86_capability);
if (c->x86 == 15) {
set_bit(X86_FEATURE_P4, c->x86_capability);
set_bit(X86_FEATURE_SYNC_RDTSC, c->x86_capability);
}
if (c->x86 == 6)
set_bit(X86_FEATURE_P3, c->x86_capability);

5
arch/x86/kernel/setup_64.c
View file

@ -888,10 +888,7 @@ static void __cpuinit init_intel(struct cpuinfo_x86 *c)
set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
if (c->x86 == 6)
set_cpu_cap(c, X86_FEATURE_REP_GOOD);
if (c->x86 == 15)
set_cpu_cap(c, X86_FEATURE_SYNC_RDTSC);
else
clear_cpu_cap(c, X86_FEATURE_SYNC_RDTSC);
set_cpu_cap(c, X86_FEATURE_LFENCE_RDTSC);
c->x86_max_cores = intel_num_cpu_cores(c);
srat_detect_node();

1
include/asm-x86/cpufeature.h
View file

@ -80,6 +80,7 @@
#define X86_FEATURE_SYNC_RDTSC (3*32+15) /* RDTSC synchronizes the CPU */
#define X86_FEATURE_REP_GOOD (3*32+16) /* rep microcode works well on this CPU */
#define X86_FEATURE_MFENCE_RDTSC (3*32+17) /* Mfence synchronizes RDTSC */
#define X86_FEATURE_LFENCE_RDTSC (3*32+18) /* Lfence synchronizes RDTSC */
/* Intel-defined CPU features, CPUID level 0x00000001 (ecx), word 4 */
#define X86_FEATURE_XMM3 (4*32+ 0) /* Streaming SIMD Extensions-3 */