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@linux.intel.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jason Baron <jbaron@redhat.com>
Link: http://lkml.kernel.org/r/1303166160-10315-4-git-send-email-hpa@linux.intel.com
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 @@
{
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