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--- arch/i386/kernel/apm.c.orig Tue Aug 14 01:39:28 2001 +++ arch/i386/kernel/apm.c Tue Sep 4 11:02:24 2001 @@ -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()) { - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Fri Sep 07 2001 - 21:00:34 EST