Ingo Molnar a écrit :
hm, this shouldnt be the case. Can you see this with -v14?
The group fairness patches fail to apply over -v14. Just to make it
clearer, I am not talking about vanilla CFS but group fairness CFS, I
have no problems with CFS.
The symptoms in the qemu box are:
o two busy loops with UID=1 remove a bit of interactivity only to UID=1
tasks
o two busy loops with UID=0 make the system unusable
Another tidbit: /proc/sched_debug now deals with users, so the task and
PID fields show some random memory garbage.
My do_div patch was nonsense (do_div returns the remainder, not the
quotient). Attached is a corrected patch.
for containers it's exactly the right behavior: group scheduling is
really a 'super' container concept that allows the allocation of CPU
time regardless of how a group uses it. The only additional control we
might want is to allocate different amount of CPU time to different
groups. (i.e. a concept vaguely similar to "nice levels", but at the
group level - using a different and saner API than nice levels.) Nice
levels are really only meaningful at the lowest level.
OK for containers, but then this should not replace the standard nice
implementation as this CPU repartition would be unexpected IMHO. I would
expect the group CPU allocation to be averaged from the nice levels of
its elements.
As a sidenote, while in CFS-v13 a nice=0 tasks seems to get 10x more CPU
than a nice=10 one, with the group fairness patch, the ratio drops to
less than 2x (for tasks with the same UID).
Regards.
--
Guillaume
--- linux/kernel/sched_fair.c
+++ linux/kernel/sched_fair.c
@@ -350,9 +350,10 @@
if (p->wait_start_fair) {
delta_fair = lrq->fair_clock - p->wait_start_fair;
- if (unlikely(p->load_weight != lrq->nice_0_load))
- delta_fair = (delta_fair * p->load_weight) /
- lrq->nice_0_load;
+ if (unlikely(p->load_weight != lrq->nice_0_load)) {
+ delta_fair *= p->load_weight;
+ do_div(delta_fair, lrq->nice_0_load);
+ }
add_wait_runtime(lrq, p, delta_fair);
}
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