Commit:     c5bcb5635a03da3158f121ae20ccbbf72b4fc62a
Parent:     9bccb23dc5fc2d268ab676e2d4212d29e230fd86
Author:     Andi Kleen <[EMAIL PROTECTED]>
AuthorDate: Wed May 2 19:27:21 2007 +0200
Committer:  Andi Kleen <[EMAIL PROTECTED]>
CommitDate: Wed May 2 19:27:21 2007 +0200

    [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" <[EMAIL PROTECTED]>
    Signed-off-by: Andi Kleen <[EMAIL PROTECTED]>
 include/asm-i386/tsc.h |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/include/asm-i386/tsc.h b/include/asm-i386/tsc.h
index 0181f9d..3f3c1fa 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:
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