Hello all,
I found that there's a possible small optimization right at the very
beginning of schedule():
if (likely(!current->exit_state)) {
if (unlikely(in_atomic())) {
can be reversed into
if (unlikely(in_atomic())) {
if (likely(!current->exit_state)) {
This is a Good Thing since it avoids having to evaluate both checks,
and both use current_thread_info() which has an inherent AGI stall risk on
x86 CPUs if it cannot be inter-mingled with other unrelated opcodes.
I'm a bit puzzled that this has not been done like that before.
Probably since the exit_state check got added as an after-thought...
Or did I miss some important reason here? (branch prediction??)
Patch against 2.6.16-rc5-mm3.
Thanks!
Signed-off-by: Andreas Mohr <[email protected]>
--- linux-2.6.16-rc5-mm3/kernel/sched.c.orig 2006-03-08 18:36:58.000000000 +0100
+++ linux-2.6.16-rc5-mm3/kernel/sched.c 2006-03-08 18:39:55.000000000 +0100
@@ -3022,8 +3022,8 @@
* 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())) {
+ if (unlikely(in_atomic())) {
+ if (likely(!current->exit_state)) {
printk(KERN_ERR "BUG: scheduling while atomic: "
"%s/0x%08x/%d\n",
current->comm, preempt_count(), current->pid);
--
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