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-rw-r--r--arch/x86/kernel/process.c29
1 files changed, 28 insertions, 1 deletions
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index c7b6a694ca22..ba370dc8685b 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -110,6 +110,33 @@ static void poll_idle(void)
cpu_relax();
}
+/*
+ * mwait selection logic:
+ *
+ * It depends on the CPU. For AMD CPUs that support MWAIT this is
+ * wrong. Family 0x10 and 0x11 CPUs will enter C1 on HLT. Powersavings
+ * then depend on a clock divisor and current Pstate of the core. If
+ * all cores of a processor are in halt state (C1) the processor can
+ * enter the C1E (C1 enhanced) state. If mwait is used this will never
+ * happen.
+ *
+ * idle=mwait overrides this decision and forces the usage of mwait.
+ */
+static int __cpuinit mwait_usable(const struct cpuinfo_x86 *c)
+{
+ if (force_mwait)
+ return 1;
+
+ if (c->x86_vendor == X86_VENDOR_AMD) {
+ switch(c->x86) {
+ case 0x10:
+ case 0x11:
+ return 0;
+ }
+ }
+ return 1;
+}
+
void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)
{
static int selected;
@@ -122,7 +149,7 @@ void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)
" performance may degrade.\n");
}
#endif
- if (cpu_has(c, X86_FEATURE_MWAIT)) {
+ if (cpu_has(c, X86_FEATURE_MWAIT) && mwait_usable(c)) {
/*
* Skip, if setup has overridden idle.
* One CPU supports mwait => All CPUs supports mwait