Commit c5bcb563 authored May 02, 2007 by Andi Kleen Committed by Andi Kleen May 02, 2007

[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>

parent 9bccb23d

include/asm-i386/tsc.h

+9 −0

Original line number	Diff line number	Diff line
		@@ -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: