[PATCH 2/6] x86: Implement support to synchronize RDTSC with LFENCE on Intel CPUs

Alok Kataria akataria at vmware.com
Wed Jun 4 00:32:28 BST 2008


OriginalAuthor: Andi Kleen <ak at suse.de>
Commit: 707fa8ed923b1b6a3d7af0d386b0b3abad28ed19

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

Signed-off-by: Alok Kataria <akataria at vmware.com>
---
 arch/x86/kernel/cpu/intel.c     |    3 ++-
 arch/x86/kernel/setup_64.c      |    5 +----
 include/asm-x86/cpufeature_32.h |    1 +
 3 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index cc8c501..161bbc0 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -201,9 +201,10 @@ 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);
diff --git a/arch/x86/kernel/setup_64.c b/arch/x86/kernel/setup_64.c
index 65b587b..7589a5d 100644
--- a/arch/x86/kernel/setup_64.c
+++ b/arch/x86/kernel/setup_64.c
@@ -816,10 +816,7 @@ static void __cpuinit init_intel(struct cpuinfo_x86 *c)
 		set_bit(X86_FEATURE_CONSTANT_TSC, &c->x86_capability);
 	if (c->x86 == 6)
 		set_bit(X86_FEATURE_REP_GOOD, &c->x86_capability);
-	if (c->x86 == 15)
-		set_bit(X86_FEATURE_SYNC_RDTSC, &c->x86_capability);
-	else
-		clear_bit(X86_FEATURE_SYNC_RDTSC, &c->x86_capability);
+	set_bit(X86_FEATURE_LFENCE_RDTSC, &c->x86_capability);
  	c->x86_max_cores = intel_num_cpu_cores(c);
 
 	srat_detect_node();
diff --git a/include/asm-x86/cpufeature_32.h b/include/asm-x86/cpufeature_32.h
index 08622c8..b8588c4 100644
--- a/include/asm-x86/cpufeature_32.h
+++ b/include/asm-x86/cpufeature_32.h
@@ -83,6 +83,7 @@
 #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 */
-- 
1.5.4






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