linux-kernel - [PATCH 0/4 TRY#3] improve alternative instruction code and optimize get_cycles

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Message-ID: <20070309150825.GA13481@amd.com>
Date:	Fri, 9 Mar 2007 16:08:25 +0100
From:	"Joerg Roedel" <joerg.roedel@....com>
To:	discuss@...-64.org
cc:	"Andi Kleen" <ak@...e.de>, linux-kernel@...r.kernel.org
Subject: [PATCH 0/4 TRY#3] improve alternative instruction code and
 optimize get_cycles_sync

This series of patches extend the alternative instructions framework on
i386 and x86_64 architectures to support two alternative instruction
replacements. This code is used together with the introduction of the
X86_FEATURE_SYNC_RDTSC flag on i386 to simplify and optimize the
get_cycles_sync() function. The optimization changes this function to
use RDTSCP instead of CPUID;RDTSC if this instruction is available.
Don't use CPUID there is really important if the kernel runs as a KVM
guest, because this instruction is intercepted and causes an expensive
VMEXIT.

Changes to the previous submit:
 * rebased to current linus git tree
 * replaced RDTSCP usage in get_cycles_sync with the opcode to
   make it compile with older binutils

-- 
Joerg Roedel
Operating System Research Center
AMD Saxony LLC & Co. KG

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