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Message-Id: <20070501035815.41DAC13CAF@wotan.suse.de> Date: Tue, 1 May 2007 05:58:15 +0200 (CEST) From: Andi Kleen <ak@...e.de> To: joerg.roedel@....com, patches@...-64.org, linux-kernel@...r.kernel.org Subject: [PATCH] [17/30] 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@....com> Signed-off-by: Andi Kleen <ak@...e.de> --- include/asm-i386/tsc.h | 9 +++++++++ 1 file changed, 9 insertions(+) Index: linux/include/asm-i386/tsc.h =================================================================== --- linux.orig/include/asm-i386/tsc.h +++ linux/include/asm-i386/tsc.h @@ -38,6 +38,15 @@ static __always_inline cycles_t get_cycl 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: */ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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