From c5bcb5635a03da3158f121ae20ccbbf72b4fc62a Mon Sep 17 00:00:00 2001 From: Andi Kleen Date: Wed, 2 May 2007 19:27:21 +0200 Subject: [PATCH] [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" Signed-off-by: Andi Kleen --- include/asm-i386/tsc.h | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/include/asm-i386/tsc.h b/include/asm-i386/tsc.h index 0181f9df75..3f3c1fa000 100644 --- a/include/asm-i386/tsc.h +++ b/include/asm-i386/tsc.h @@ -37,6 +37,15 @@ static __always_inline cycles_t get_cycles_sync(void) unsigned long long ret; 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: -- 2.39.5