Merge commit 'linus/master' into sched-fixes-for-linus

[linux-2.6] / arch / x86 / kernel / process.c

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index c7b6a694ca22c3746d8f245ef98dc3e507442961..ba370dc8685bf8f9bf31e9100f78c4e800ea755e 100644 (file)
--- 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