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| author |   Andi Kleen <ak@suse.de> | 2007-05-02 19:27:21 +0200 |
|---|---|---|
| committer |   Andi Kleen <andi@basil.nowhere.org> | 2007-05-02 19:27:21 +0200 |
| commit | c5bcb5635a03da3158f121ae20ccbbf72b4fc62a (patch) | |
| tree | a69fff3138ad14a7949d979f2d2e5893c5cb77de | |
| parent | [PATCH] i386: Add X86_FEATURE_RDTSCP (diff) | |
| download | linux-dev-c5bcb5635a03da3158f121ae20ccbbf72b4fc62a.tar.xz linux-dev-c5bcb5635a03da3158f121ae20ccbbf72b4fc62a.zip | |
[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>
| -rw-r--r-- | 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 0181f9df7539..3f3c1fa000b4 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: */ |