Commit-ID: d8d9766c8c29f71c37bc4b74cc9fcf6a192c9bfd
Gitweb: http://git.kernel.org/tip/d8d9766c8c29f71c37bc4b74cc9fcf6a192c9bfd
Author: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
AuthorDate: Mon, 18 Apr 2011 15:31:57 -0700
Committer: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Jason Baron <jbaron@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/1303166160-10315-4-git-send-email-hpa@xxxxxxxxxxxxxxx
---
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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