x86: Simplify cpu_idle_wait

This patch also resolves hangs on boot:
	http://lkml.org/lkml/2008/2/23/263
	http://bugzilla.kernel.org/show_bug.cgi?id=10093

The bug was causing once-in-few-reboots 10-15 sec wait during boot on
certain laptops.

Earlier commit 40d6a146629b98d8e322b6f9332b182c7cbff3df added
smp_call_function in cpu_idle_wait() to kick cpus that are in tickless
idle.  Looking at cpu_idle_wait code at that time, code seemed to be
over-engineered for a case which is rarely used (while changing idle
handler).

Below is a simplified version of cpu_idle_wait, which just makes a dummy
smp_call_function to all cpus, to make them come out of old idle handler
and start using the new idle handler.  It eliminates code in the idle
loop to handle cpu_idle_wait.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 11 insertions, 36 deletions

diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index be3c7a299f02..43930e73f657 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -82,7 +82,6 @@ unsigned long thread_saved_pc(struct task_struct *tsk)
  */
 void (*pm_idle)(void);
 EXPORT_SYMBOL(pm_idle);
-static DEFINE_PER_CPU(unsigned int, cpu_idle_state);
 
 void disable_hlt(void)
 {
@@ -190,9 +189,6 @@ void cpu_idle(void)
                 while (!need_resched()) {
                         void (*idle)(void);
 
-                        if (__get_cpu_var(cpu_idle_state))
-                                __get_cpu_var(cpu_idle_state) = 0;
-
                         check_pgt_cache();
                         rmb();
                         idle = pm_idle;
@@ -220,40 +216,19 @@ 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)
 {
-        unsigned int cpu, this_cpu = get_cpu();
-        cpumask_t map, tmp = current->cpus_allowed;
-
-        set_cpus_allowed(current, cpumask_of_cpu(this_cpu));
-        put_cpu();
-
-        cpus_clear(map);
-        for_each_online_cpu(cpu) {
-                per_cpu(cpu_idle_state, cpu) = 1;
-                cpu_set(cpu, map);
-        }
-
-        __get_cpu_var(cpu_idle_state) = 0;
-
-        wmb();
-        do {
-                ssleep(1);
-                for_each_online_cpu(cpu) {
-                        if (cpu_isset(cpu, map) && !per_cpu(cpu_idle_state, cpu))
-                                cpu_clear(cpu, map);
-                }
-                cpus_and(map, map, cpu_online_map);
-                /*
-                 * We waited 1 sec, if a CPU still did not call idle
-                 * it may be because it is in idle and not waking up
-                 * because it has nothing to do.
-                 * Give all the remaining CPUS a kick.
-                 */
-                smp_call_function_mask(map, do_nothing, NULL, 0);
-        } while (!cpus_empty(map));
-
-        set_cpus_allowed(current, tmp);
+        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);