linux-kernel - [PATCH 3/3] x86, cpu: Change NOP selection for certain Intel CPUs

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Date:	Mon, 18 Apr 2011 15:36:00 -0700
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	linux-kernel@...r.kernel.org
Cc:	Jason Baron <jbaron@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>, tglx@...utronix.de,
	mingo@...e.hu, "H. Peter Anvin" <hpa@...ux.intel.com>,
	Tejun Heo <tj@...nel.org>
Subject: [PATCH 3/3] 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>
---
 arch/x86/kernel/alternative.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 2ca3f65..34bf87e 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -190,7 +190,14 @@ void __init arch_init_ideal_nops(void)
 {
 	switch (boot_cpu_data.x86_vendor) {
 	case X86_VENDOR_INTEL:
-		if (boot_cpu_has(X86_FEATURE_NOPL)) {
+		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
-- 
1.7.3.4

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