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authorAndi Kleen <ak@suse.de>2008-01-30 13:32:38 +0100
committerIngo Molnar <mingo@elte.hu>2008-01-30 13:32:38 +0100
commitfde1b3fa947c2512e3715962ebb1d3a6a9b9bb7d (patch)
tree48ad640f75034747187f98fa0040897639376fb6
parent2a10e7c41254941cac87be1eccdcb6379ce097f5 (diff)
x86: introduce rdtsc_barrier()
rdtsc_barrier() is a new barrier primitive that stops RDTSC speculation to avoid races with timer interrupts on other CPUs. It expands either to LFENCE (for Intel CPUs) or MFENCE (for AMD CPUs) which stops RDTSC on all currently known microarchitectures that implement SSE. On CPUs without SSE there is generally no RDTSC speculation. [ mingo@elte.hu: renamed it to rdtsc_barrier() and made it x86-only ] Signed-off-by: Andi Kleen <ak@suse.de> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
-rw-r--r--include/asm-x86/system.h13
1 files changed, 13 insertions, 0 deletions
diff --git a/include/asm-x86/system.h b/include/asm-x86/system.h
index 6c7d1fda499..39474f2957a 100644
--- a/include/asm-x86/system.h
+++ b/include/asm-x86/system.h
@@ -5,6 +5,7 @@
#include <asm/segment.h>
#include <asm/cpufeature.h>
#include <asm/cmpxchg.h>
+#include <asm/nops.h>
#include <linux/kernel.h>
#include <linux/irqflags.h>
@@ -395,5 +396,17 @@ void default_idle(void);
#define set_mb(var, value) do { var = value; barrier(); } while (0)
#endif
+/*
+ * Stop RDTSC speculation. This is needed when you need to use RDTSC
+ * (or get_cycles or vread that possibly accesses the TSC) in a defined
+ * code region.
+ *
+ * (Could use an alternative three way for this if there was one.)
+ */
+static inline void rdtsc_barrier(void)
+{
+ alternative(ASM_NOP3, "mfence", X86_FEATURE_MFENCE_RDTSC);
+ alternative(ASM_NOP3, "lfence", X86_FEATURE_LFENCE_RDTSC);
+}
#endif