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authorAndi Kleen <ak@suse.de>2007-05-02 19:27:21 +0200
committerAndi Kleen <andi@basil.nowhere.org>2007-05-02 19:27:21 +0200
commitc5bcb5635a03da3158f121ae20ccbbf72b4fc62a (patch)
treea69fff3138ad14a7949d979f2d2e5893c5cb77de /include/asm-i386/tsc.h
parent9bccb23dc5fc2d268ab676e2d4212d29e230fd86 (diff)
[PATCH] x86: Use RDTSCP for synchronous get_cycles if possible
RDTSCP is already synchronous and doesn't need an explicit CPUID. This is a little faster and more importantly avoids VMEXITs on Hypervisors. Original patch from Joerg Roedel, but reworked by AK Also includes miscompilation fix by Eric Biederman Cc: "Joerg Roedel" <joerg.roedel@amd.com> Signed-off-by: Andi Kleen <ak@suse.de>
Diffstat (limited to 'include/asm-i386/tsc.h')
-rw-r--r--include/asm-i386/tsc.h9
1 files changed, 9 insertions, 0 deletions
diff --git a/include/asm-i386/tsc.h b/include/asm-i386/tsc.h
index 0181f9df753..3f3c1fa000b 100644
--- a/include/asm-i386/tsc.h
+++ b/include/asm-i386/tsc.h
@@ -38,6 +38,15 @@ static __always_inline cycles_t get_cycles_sync(void)
unsigned eax;
/*
+ * Use RDTSCP if possible; it is guaranteed to be synchronous
+ * and doesn't cause a VMEXIT on Hypervisors
+ */
+ alternative_io(ASM_NOP3, ".byte 0x0f,0x01,0xf9", X86_FEATURE_RDTSCP,
+ "=A" (ret), "0" (0ULL) : "ecx", "memory");
+ if (ret)
+ return ret;
+
+ /*
* Don't do an additional sync on CPUs where we know
* RDTSC is already synchronous:
*/