This fix is needed for AMD family 10h CPUs.
It prevents auto select of mwait_idle for AMD CPUs.
MWAIT does not enter C-states on family 10h and more
power saving is reached by entering C1 with
default_idle.
The patch also adds an idle=mwait command line option
to select mwait_idle for benchmarking.
Signed-off-by: Andreas Herrmann <[email protected]>
---
arch/x86_64/kernel/process.c | 9 +++++++--
arch/x86_64/kernel/setup.c | 4 ++++
include/asm-x86_64/cpufeature.h | 1 +
3 files changed, 12 insertions(+), 2 deletions(-)
diff --git a/arch/x86_64/kernel/process.c b/arch/x86_64/kernel/process.c
index d8d5ccc..18fe9de 100644
--- a/arch/x86_64/kernel/process.c
+++ b/arch/x86_64/kernel/process.c
@@ -271,7 +271,8 @@ static void mwait_idle(void)
void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)
{
static int printed;
- if (cpu_has(c, X86_FEATURE_MWAIT)) {
+ if (cpu_has(c, X86_FEATURE_MWAIT) &&
+ !cpu_has(c, X86_FEATURE_MWAIT_NO_CSTATE)) {
/*
* Skip, if setup has overridden idle.
* One CPU supports mwait => All CPUs supports mwait
@@ -291,7 +292,11 @@ static int __init idle_setup (char *str)
if (!strncmp(str, "poll", 4)) {
printk("using polling idle threads.\n");
pm_idle = poll_idle;
- }
+ } else if (!strncmp(str, "mwait", 5))
+ if (boot_cpu_has(X86_FEATURE_MWAIT)) {
+ printk(KERN_INFO "using mwait in idle threads.\n");
+ pm_idle = mwait_idle;
+ }
boot_option_idle_override = 1;
return 1;
diff --git a/arch/x86_64/kernel/setup.c b/arch/x86_64/kernel/setup.c
index 3d98b69..b707025 100644
--- a/arch/x86_64/kernel/setup.c
+++ b/arch/x86_64/kernel/setup.c
@@ -612,6 +612,10 @@ static void __cpuinit init_amd(struct cpuinfo_x86 *c)
/* RDTSC can be speculated around */
clear_bit(X86_FEATURE_SYNC_RDTSC, &c->x86_capability);
+
+ /* prevent auto select of mwait_idle */
+ if (cpu_has(c, X86_FEATURE_MWAIT))
+ set_bit(X86_FEATURE_MWAIT_NO_CSTATE, c->x86_capability);
}
static void __cpuinit detect_ht(struct cpuinfo_x86 *c)
diff --git a/include/asm-x86_64/cpufeature.h b/include/asm-x86_64/cpufeature.h
index 0b3c686..9331d1a 100644
--- a/include/asm-x86_64/cpufeature.h
+++ b/include/asm-x86_64/cpufeature.h
@@ -70,6 +70,7 @@
#define X86_FEATURE_ARCH_PERFMON (3*32+9) /* Intel Architectural PerfMon */
#define X86_FEATURE_PEBS (3*32+10) /* Precise-Event Based Sampling */
#define X86_FEATURE_BTS (3*32+11) /* Branch Trace Store */
+#define X86_FEATURE_MWAIT_NO_CSTATE (3*32+12) /* mwait does not enter c-state */
/* Intel-defined CPU features, CPUID level 0x00000001 (ecx), word 4 */
#define X86_FEATURE_XMM3 (4*32+ 0) /* Streaming SIMD Extensions-3 */
--
1.5.0.6
-
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