1 files changed, 117 insertions, 0 deletions

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 3004d716539d..67e9b4a1e89d 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -4,6 +4,8 @@
 #include <linux/smp.h>
 #include <linux/slab.h>
 #include <linux/sched.h>
+#include <linux/module.h>
+#include <linux/pm.h>
 
 struct kmem_cache *task_xstate_cachep;
 
@@ -42,3 +44,118 @@ void arch_task_cache_init(void)
                                   __alignof__(union thread_xstate),
                                   SLAB_PANIC, NULL);
 }
+
+static void do_nothing(void *unused)
+{
+}
+
+/*
+ * cpu_idle_wait - Used to ensure that all the CPUs discard old value of
+ * pm_idle and update to new pm_idle value. Required while changing pm_idle
+ * handler on SMP systems.
+ *
+ * Caller must have changed pm_idle to the new value before the call. Old
+ * pm_idle value will not be used by any CPU after the return of this function.
+ */
+void cpu_idle_wait(void)
+{
+        smp_mb();
+        /* kick all the CPUs so that they exit out of pm_idle */
+        smp_call_function(do_nothing, NULL, 0, 1);
+}
+EXPORT_SYMBOL_GPL(cpu_idle_wait);
+
+/*
+ * This uses new MONITOR/MWAIT instructions on P4 processors with PNI,
+ * which can obviate IPI to trigger checking of need_resched.
+ * We execute MONITOR against need_resched and enter optimized wait state
+ * through MWAIT. Whenever someone changes need_resched, we would be woken
+ * up from MWAIT (without an IPI).
+ *
+ * New with Core Duo processors, MWAIT can take some hints based on CPU
+ * capability.
+ */
+void mwait_idle_with_hints(unsigned long ax, unsigned long cx)
+{
+        if (!need_resched()) {
+                __monitor((void *)&current_thread_info()->flags, 0, 0);
+                smp_mb();
+                if (!need_resched())
+                        __mwait(ax, cx);
+        }
+}
+
+/* Default MONITOR/MWAIT with no hints, used for default C1 state */
+static void mwait_idle(void)
+{
+        if (!need_resched()) {
+                __monitor((void *)&current_thread_info()->flags, 0, 0);
+                smp_mb();
+                if (!need_resched())
+                        __sti_mwait(0, 0);
+                else
+                        local_irq_enable();
+        } else
+                local_irq_enable();
+}
+
+
+static int __cpuinit mwait_usable(const struct cpuinfo_x86 *c)
+{
+        if (force_mwait)
+                return 1;
+        /* Any C1 states supported? */
+        return c->cpuid_level >= 5 && ((cpuid_edx(5) >> 4) & 0xf) > 0;
+}
+
+/*
+ * On SMP it's slightly faster (but much more power-consuming!)
+ * to poll the ->work.need_resched flag instead of waiting for the
+ * cross-CPU IPI to arrive. Use this option with caution.
+ */
+static void poll_idle(void)
+{
+        local_irq_enable();
+        cpu_relax();
+}
+
+void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)
+{
+        static int selected;
+
+        if (selected)
+                return;
+#ifdef CONFIG_X86_SMP
+        if (pm_idle == poll_idle && smp_num_siblings > 1) {
+                printk(KERN_WARNING "WARNING: polling idle and HT enabled,"
+                        " performance may degrade.\n");
+        }
+#endif
+        if (cpu_has(c, X86_FEATURE_MWAIT) && mwait_usable(c)) {
+                /*
+                 * Skip, if setup has overridden idle.
+                 * One CPU supports mwait => All CPUs supports mwait
+                 */
+                if (!pm_idle) {
+                        printk(KERN_INFO "using mwait in idle threads.\n");
+                        pm_idle = mwait_idle;
+                }
+        }
+        selected = 1;
+}
+
+static int __init idle_setup(char *str)
+{
+        if (!strcmp(str, "poll")) {
+                printk("using polling idle threads.\n");
+                pm_idle = poll_idle;
+        } else if (!strcmp(str, "mwait"))
+                force_mwait = 1;
+        else
+                return -1;
+
+        boot_option_idle_override = 1;
+        return 0;
+}
+early_param("idle", idle_setup);
+