[PATCH] Fix idle notifiers

Previously exit_idle would be called more often than enter_idle

Now instead of using complicated tests just keep track of it
using the per CPU variable as a flip flop.  I moved the idle state into the
PDA to make the access more efficient.

Original bug report and an initial patch from Stephane Eranian,
but redone by AK.

Cc: Stephane Eranian <eranian@hpl.hp.com>

Signed-off-by: Andi Kleen <ak@suse.de>

1 files changed, 9 insertions, 6 deletions

diff --git a/arch/x86_64/kernel/process.c b/arch/x86_64/kernel/process.c
index 885c318f76ab..458006ae19f3 100644
--- a/arch/x86_64/kernel/process.c
+++ b/arch/x86_64/kernel/process.c
@@ -80,25 +80,25 @@ void idle_notifier_unregister(struct notifier_block *n)
 }
 EXPORT_SYMBOL(idle_notifier_unregister);
 
-enum idle_state { CPU_IDLE, CPU_NOT_IDLE };
-static DEFINE_PER_CPU(enum idle_state, idle_state) = CPU_NOT_IDLE;
-
 void enter_idle(void)
 {
-        __get_cpu_var(idle_state) = CPU_IDLE;
+        write_pda(isidle, 1);
         atomic_notifier_call_chain(&idle_notifier, IDLE_START, NULL);
 }
 
 static void __exit_idle(void)
 {
-        __get_cpu_var(idle_state) = CPU_NOT_IDLE;
+        if (read_pda(isidle) == 0)
+                return;
+        write_pda(isidle, 0);
         atomic_notifier_call_chain(&idle_notifier, IDLE_END, NULL);
 }
 
 /* Called from interrupts to signify idle end */
 void exit_idle(void)
 {
-        if (current->pid | read_pda(irqcount))
+        /* idle loop has pid 0 */
+        if (current->pid)
                 return;
         __exit_idle();
 }
@@ -220,6 +220,9 @@ void cpu_idle (void)
                                 play_dead();
                         enter_idle();
                         idle();
+                        /* In many cases the interrupt that ended idle
+                           has already called exit_idle. But some idle
+                           loops can be woken up without interrupt. */
                         __exit_idle();
                 }