From: Bill Burns <bburns@redhat.com>
Date: Tue, 18 Mar 2008 15:24:23 -0400
Subject: Revert: [xen] idle=poll instead of hypercall block
Message-id: 47E016E7.8000809@redhat.com
O-Subject: [RHEL5.2] Fix xen kenel Timer ISR/0: Time went backwards
Bugzilla: 437252

Fixes 437252

On certain systems (levovo t60 for one) booting the Xen kernel
results in timer went backwards messages, soft lockups and overall
horrid performance. The issue was introduced by a change that
allows substitution of the idle loop for xenoprofile. (bz 416141).

The patch for 416141, used an existing variable pm_idle to hold the
idle routine address. In the presence of a boot arg an
alternate idle loop could be chosen. The intent of the patch
was to allow one of two idle loops to be used for the Xen
kernel.

Previsouly, for the Xen kernel, this variable was provided
but unused. For bare metal kernels this variable
is used by other code to change the idle routine. Using this
variable in Xen allowed setting an improper idle routine
for the Xen kernel.

While the original patch could be simply fixed to
avoid this, the safest change at this point is to revert the
patch. The patch submitter for 416141 fully agrees.

The fix to this issue is to remove patch:

Patch22307: linux-2.6-xen-idle-poll-instead-of-hypercall-block.patch

Please review and ack.

 Bill

Acked-by: "Stephen C. Tweedie" <sct@redhat.com>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>

diff --git a/arch/i386/kernel/process-xen.c b/arch/i386/kernel/process-xen.c
index 11522ba..6cad288 100644
--- a/arch/i386/kernel/process-xen.c
+++ b/arch/i386/kernel/process-xen.c
@@ -96,24 +96,8 @@ void enable_hlt(void)
 
 EXPORT_SYMBOL(enable_hlt);
 
-/*
- * 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)
+/* XXX XEN doesn't use default_idle(), poll_idle(). Use xen_idle() instead. */
+void xen_idle(void)
 {
 	local_irq_disable();
 
@@ -164,22 +148,17 @@ void cpu_idle(void)
 	/* endless idle loop with no priority at all */
 	while (1) {
 		while (!need_resched()) {
-			void (*idle)(void);
 
 			if (__get_cpu_var(cpu_idle_state))
 				__get_cpu_var(cpu_idle_state) = 0;
 
 			rmb();
-			idle = pm_idle;
-
-			if (!idle)
-				idle = xen_idle;
 
 			if (cpu_is_offline(cpu))
 				play_dead();
 
 			__get_cpu_var(irq_stat).idle_timestamp = jiffies;
-			idle();
+			xen_idle();
 		}
 		preempt_enable_no_resched();
 		schedule();
@@ -215,22 +194,9 @@ void cpu_idle_wait(void)
 }
 EXPORT_SYMBOL_GPL(cpu_idle_wait);
 
-void __devinit select_idle_routine(const struct cpuinfo_x86 *c)
-{
-}
-
-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);
+/* 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 show_regs(struct pt_regs * regs)
 {
diff --git a/arch/x86_64/kernel/process-xen.c b/arch/x86_64/kernel/process-xen.c
index 4d40a58..fc34b29 100644
--- a/arch/x86_64/kernel/process-xen.c
+++ b/arch/x86_64/kernel/process-xen.c
@@ -111,26 +111,8 @@ void exit_idle(void)
 	__exit_idle();
 }
 
-/*
- * 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)
+/* XXX XEN doesn't use default_idle(), poll_idle(). Use xen_idle() instead. */
+void xen_idle(void)
 {
 	local_irq_disable();
 
@@ -173,18 +155,14 @@ void cpu_idle (void)
 	/* endless idle loop with no priority at all */
 	while (1) {
 		while (!need_resched()) {
-			void (*idle)(void);
-
 			if (__get_cpu_var(cpu_idle_state))
 				__get_cpu_var(cpu_idle_state) = 0;
 			rmb();
-			idle = pm_idle;
-			if (!idle)
-				idle = xen_idle;
+			
 			if (cpu_is_offline(smp_processor_id()))
 				play_dead();
 			enter_idle();
-			idle();
+			xen_idle();
 			__exit_idle();
 		}
 
@@ -223,22 +201,9 @@ void cpu_idle_wait(void)
 }
 EXPORT_SYMBOL_GPL(cpu_idle_wait);
 
-void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c) 
-{
-}
-
-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);
+/* 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) {}
 
 /* Prints also some state that isn't saved in the pt_regs */ 
 void __show_regs(struct pt_regs * regs)