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

[H. Peter Anvin]

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@xxxxxxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Jason Baron <jbaron@xxxxxxxxxx>
---
 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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/