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Commit 707fa8ed authored by Andi Kleen's avatar Andi Kleen Committed by Ingo Molnar
Browse files

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



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: default avatarAndi Kleen <ak@suse.de>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent de421863

arch/x86/kernel/cpu/intel.c

+2 −1
Original line number Diff line number Diff line
@@ -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);

arch/x86/kernel/setup_64.c

+1 −4
Original line number Diff line number Diff line
@@ -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();

include/asm-x86/cpufeature.h

+1 −0
Original line number Diff line number Diff line
@@ -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 */