On Mon, 2008-01-28 at 21:13 +0100, Guillaume Chazarain wrote:
> Unfortunately it seems to not be completely fixed, with this script:
>
> #!/usr/bin/python
>
> import os
> import time
>
> SLEEP_TIME = 0.1
> SAMPLES = 5
> PRINT_DELAY = 0.5
>
> def print_wakeup_latency():
> times = []
> last_print = 0
> while True:
> start = time.time()
> time.sleep(SLEEP_TIME)
> end = time.time()
> times.insert(0, end - start - SLEEP_TIME)
> del times[SAMPLES:]
> if end > last_print + PRINT_DELAY:
> copy = times[:]
> copy.sort()
> print '%f ms' % (copy[len(copy)/2] * 1000)
> last_print = end
>
> if os.fork() == 0:
> if os.fork() == 0:
> os.setuid(1)
> while True:
> pass
> else:
> os.setuid(2)
> while True:
> pass
> else:
> os.setuid(1)
> print_wakeup_latency()
>
> I get seemingly unpredictable latencies (with or without the patch applied):
>
> # ./sched.py
> 14.810944 ms
> 19.829893 ms
> 1.968050 ms
> 8.021021 ms
> -0.017977 ms
> 4.926109 ms
> 11.958027 ms
> 5.995893 ms
> 1.992130 ms
> 0.007057 ms
> 0.217819 ms
> -0.004864 ms
> 5.907202 ms
> 6.547832 ms
> -0.012970 ms
> 0.209951 ms
> -0.002003 ms
> 4.989052 ms
>
> Without FAIR_USER_SCHED, latencies are consistently in the noise.
> Also, I forgot to mention that I'm on a single CPU.
>
> Thanks for the help.
Does something like this help?
Index: linux-2.6/kernel/sched_fair.c
===================================================================
--- linux-2.6.orig/kernel/sched_fair.c
+++ linux-2.6/kernel/sched_fair.c
@@ -267,8 +267,12 @@ static u64 sched_slice(struct cfs_rq *cf
{
u64 slice = __sched_period(cfs_rq->nr_running);
- slice *= se->load.weight;
- do_div(slice, cfs_rq->load.weight);
+ for_each_sched_entity(se) {
+ cfs_rq = cfs_rq_of(se);
+
+ slice *= se->load.weight;
+ do_div(slice, cfs_rq->load.weight);
+ }
return slice;
}
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