linux-kernel - [tip:x86/cpu] x86, cpu: Change NOP selection for certain Intel CPUs

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Message-ID: <tip-d8d9766c8c29f71c37bc4b74cc9fcf6a192c9bfd@git.kernel.org>
Date:	Tue, 19 Apr 2011 01:02:02 GMT
From:	"tip-bot for H. Peter Anvin" <hpa@...ux.intel.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	fweisbec@...il.com, rostedt@...dmis.org, tj@...nel.org,
	tglx@...utronix.de, jbaron@...hat.com, hpa@...ux.intel.com
Subject: [tip:x86/cpu] x86, cpu: Change NOP selection for certain Intel CPUs

Commit-ID:  d8d9766c8c29f71c37bc4b74cc9fcf6a192c9bfd
Gitweb:     http://git.kernel.org/tip/d8d9766c8c29f71c37bc4b74cc9fcf6a192c9bfd
Author:     H. Peter Anvin <hpa@...ux.intel.com>
AuthorDate: Mon, 18 Apr 2011 15:31:57 -0700
Committer:  H. Peter Anvin <hpa@...ux.intel.com>
CommitDate: Mon, 18 Apr 2011 16:40:32 -0700

x86, cpu: Change NOP selection for certain Intel CPUs

Due to a decoder implementation quirk, some specific Intel CPUs
actually perform better with the "k8_nops" than with the
SDM-recommended NOPs.  For runtime-selected NOPs, if we detect those
specific CPUs then use the k8_nops instead of the ones we would
normally use.

Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
Cc: Tejun Heo <tj@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Jason Baron <jbaron@...hat.com>
Link: http://lkml.kernel.org/r/1303166160-10315-4-git-send-email-hpa@linux.intel.com
---
 arch/x86/kernel/alternative.c |   14 +++++++++++++-
 1 files changed, 13 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 846f61e..c0501ea 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -199,7 +199,19 @@ void __init arch_init_ideal_nops(void)
 {
 	switch (boot_cpu_data.x86_vendor) {
 	case X86_VENDOR_INTEL:
-		if (boot_cpu_has(X86_FEATURE_NOPL)) {
+		/*
+		 * Due to a decoder implementation quirk, some
+		 * specific Intel CPUs actually perform better with
+		 * the "k8_nops" than with the SDM-recommended NOPs.
+		 */
+		if (boot_cpu_data.x86 == 6 &&
+		    boot_cpu_data.x86_model >= 0x0f &&
+		    boot_cpu_data.x86_model != 0x1c &&
+		    boot_cpu_data.x86_model != 0x26 &&
+		    boot_cpu_data.x86_model != 0x27 &&
+		    boot_cpu_data.x86_model < 0x30) {
+			ideal_nops = k8_nops;
+		} else if (boot_cpu_has(X86_FEATURE_NOPL)) {
 			   ideal_nops = p6_nops;
 		} else {
 #ifdef CONFIG_X86_64
--
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