[LINUX] Implement the idle=poll option in the kernel when running on Xen.

This causes the kernel to use a polling loop rather than hypercall
down to block. I have found this useful to profile the amount of sleep
cycles when using xenoprof, there may be other uses.

Signed-off-by: Amitabha Roy <amitabha.roy@gmail.com>

2 files changed, 76 insertions, 12 deletions

diff --git a/linux-2.6-xen-sparse/arch/i386/kernel/process-xen.c b/linux-2.6-xen-sparse/arch/i386/kernel/process-xen.c
index e6724a00b1..00a8d8a8eb 100644
--- a/linux-2.6-xen-sparse/arch/i386/kernel/process-xen.c
+++ b/linux-2.6-xen-sparse/arch/i386/kernel/process-xen.c
@@ -101,8 +101,24 @@ void enable_hlt(void)
 
 EXPORT_SYMBOL(enable_hlt);
 
-/* XXX XEN doesn't use default_idle(), poll_idle(). Use xen_idle() instead. */
-void xen_idle(void)
+/*
+ * 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();
+
+	asm volatile(
+		"2:"
+		"testl %0, %1;"
+		"rep; nop;"
+		"je 2b;"
+		: : "i"(_TIF_NEED_RESCHED), "m" (current_thread_info()->flags));
+}
+
+static void xen_idle(void)
 {
 	local_irq_disable();
 
@@ -162,7 +178,7 @@ void cpu_idle(void)
 				play_dead();
 
 			__get_cpu_var(irq_stat).idle_timestamp = jiffies;
-			xen_idle();
+			pm_idle();
 		}
 		preempt_enable_no_resched();
 		schedule();
@@ -198,9 +214,24 @@ void cpu_idle_wait(void)
 }
 EXPORT_SYMBOL_GPL(cpu_idle_wait);
 
-/* XXX XEN doesn't use mwait_idle(), select_idle_routine(), idle_setup(). */
-/* Always use xen_idle() instead. */
-void __devinit select_idle_routine(const struct cpuinfo_x86 *c) {}
+void __devinit select_idle_routine(const struct cpuinfo_x86 *c)
+{
+	if (!pm_idle)
+		pm_idle = xen_idle;
+}
+
+static int __init idle_setup (char *str)
+{
+	if (!strncmp(str, "poll", 4)) {
+		printk("using polling idle threads.\n");
+		pm_idle = poll_idle;
+	}
+
+	boot_option_idle_override = 1;
+	return 1;
+}
+
+__setup("idle=", idle_setup);
 
 void show_regs(struct pt_regs * regs)
 {
diff --git a/linux-2.6-xen-sparse/arch/x86_64/kernel/process-xen.c b/linux-2.6-xen-sparse/arch/x86_64/kernel/process-xen.c
index 65ba83c625..c12ebe0e01 100644
--- a/linux-2.6-xen-sparse/arch/x86_64/kernel/process-xen.c
+++ b/linux-2.6-xen-sparse/arch/x86_64/kernel/process-xen.c
@@ -119,8 +119,26 @@ void exit_idle(void)
 	__exit_idle();
 }
 
-/* XXX XEN doesn't use default_idle(), poll_idle(). Use xen_idle() instead. */
-void xen_idle(void)
+/*
+ * On SMP it's slightly faster (but much more power-consuming!)
+ * to poll the ->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();
+
+	asm volatile(
+		"2:"
+		"testl %0,%1;"
+		"rep; nop;"
+		"je 2b;"
+		: :
+		"i" (_TIF_NEED_RESCHED),
+		"m" (current_thread_info()->flags));
+}
+
+static void xen_idle(void)
 {
 	local_irq_disable();
 
@@ -171,7 +189,7 @@ void cpu_idle (void)
 			if (cpu_is_offline(smp_processor_id()))
 				play_dead();
 			enter_idle();
-			xen_idle();
+			pm_idle();
 			__exit_idle();
 		}
 
@@ -210,9 +228,24 @@ void cpu_idle_wait(void)
 }
 EXPORT_SYMBOL_GPL(cpu_idle_wait);
 
-/* XXX XEN doesn't use mwait_idle(), select_idle_routine(), idle_setup(). */
-/* Always use xen_idle() instead. */
-void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c) {}
+void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c) 
+{
+	if (!pm_idle)
+		pm_idle = xen_idle;
+}
+
+static int __init idle_setup (char *str)
+{
+	if (!strncmp(str, "poll", 4)) {
+		printk("using polling idle threads.\n");
+		pm_idle = poll_idle;
+	}
+
+	boot_option_idle_override = 1;
+	return 1;
+}
+
+__setup("idle=", idle_setup);
 
 /* Prints also some state that isn't saved in the pt_regs */ 
 void __show_regs(struct pt_regs * regs)