kapmd improvent?

The problem:

After a burst of heavy load my system (a laptop) returns idle, but kapmd isn't scheduled anymore so if I 'top' I can see the system nearly 100% idle but kampd is consuming 0.0% CPU time.

The explanation:

when kapmd returns from schedule_timeout it checks if system_idle(), at this point if there is more than one task running we double timeout (clamp it to APM_CHECK_TIMEOUT) and go to sleep;
Q: what if there are tasks that are always
running when we try to call apm_do_idle ?
A: we never enter the kapmd inner loop.

the ?solution?:
make the timeout short if we find that the system is busy, some tries later if the system is idle enough we will enter the kapmd inner loop and do some power mgt.

Alternative solution instead of setting timeout to 1 we could

timeout >>= 2; /divide by 4
and clamp the value to 1 if it becomes 0

So the timeout changes smoothly.

On my system this makes kapmd come back fast.(without evil side effects, I hope ;) )

Let me know if this is useful somehow.

the patch is against vanilla 2.4.9

Regards

--
Delio

@@ -1136,8 +1136,10 @@
 		set_current_state(TASK_INTERRUPTIBLE);
 		apm_event_handler();
 #ifdef CONFIG_APM_CPU_IDLE
-		if (!system_idle())
+		if (!system_idle()) {
+			timeout = 1;
 			continue;
+		}
 		if (apm_do_idle()) {
 			unsigned long start = jiffies;
 			while ((!exit_kapmd) && system_idle()) {