Re: [PATCH] -mm: Small schedule() optimization

[Ingo Molnar <mingo@elte.hu>]

* Con Kolivas <kernel@kolivas.org> wrote:

> > -	if (likely(!current->exit_state)) {
> > -		if (unlikely(in_atomic())) {
> > +	if (unlikely(in_atomic())) {
> > +		if (likely(!current->exit_state)) {
> 
> I suspect that once we're in_atomic() then we're no longer likely to 
> be !current->exit_state
> 
> Probably better to just
> 	if (unlikely(in_atomic())) {
> 		if (!current->exit_state) {
> 
> Ingo?

yeah. There's not much point in nesting likely/unlikely. In fact we can 
just merge the two conditions, as per updated patch below.

	Ingo

---
From: Andreas Mohr <andi@lisas.de>

small schedule() microoptimization.

Signed-off-by: Andreas Mohr <andi@lisas.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

--- linux/kernel/sched.c.orig
+++ linux/kernel/sched.c
@@ -2873,13 +2873,11 @@ asmlinkage void __sched schedule(void)
 	 * schedule() atomically, we ignore that path for now.
 	 * Otherwise, whine if we are scheduling when we should not be.
 	 */
-	if (likely(!current->exit_state)) {
-		if (unlikely(in_atomic())) {
-			printk(KERN_ERR "scheduling while atomic: "
-				"%s/0x%08x/%d\n",
-				current->comm, preempt_count(), current->pid);
-			dump_stack();
-		}
+	if (unlikely(in_atomic() && !current->exit_state)) {
+		printk(KERN_ERR "scheduling while atomic: "
+			"%s/0x%08x/%d\n",
+			current->comm, preempt_count(), current->pid);
+		dump_stack();
 	}
 	profile_hit(SCHED_PROFILING, __builtin_return_address(0));