Messages in this thread | | | Subject | Re: scheduler oddity [bug?] | From | Mike Galbraith <> | Date | Sun, 08 Mar 2009 17:20:00 +0100 |
| |
On Sun, 2009-03-08 at 16:39 +0100, Ingo Molnar wrote: > * Mike Galbraith <efault@gmx.de> wrote: > > > The problem with your particular testcase is that while one > > half has an avg_overlap (what we use as affinity hint for > > synchronous wakeups) which triggers the affinity hint, the > > other half has avg_overlap of zero, what it was born with, so > > despite significant execution overlap, the scheduler treats > > them as if they were truly synchronous tasks. > > hm, why does it stay on zero?
Wakeup preemption. Presuming here: heavy task wakes light task, is preempted, light task stuffs data into pipe, heavy task doesn't block, so no avg_overlap is ever computed. The heavy task uses 100% CPU.
Running as SCHED_BATCH (virgin source), it becomes sane.
pipetest (6836, #threads: 1) --------------------------------------------------------- se.exec_start : 266073.001296 se.vruntime : 173620.953443 se.sum_exec_runtime : 11324.486321 se.avg_overlap : 1.306762 nr_switches : 381 nr_voluntary_switches : 2 nr_involuntary_switches : 379 se.load.weight : 1024 policy : 3 prio : 120 clock-delta : 109
pipetest (6837, #threads: 1) --------------------------------------------------------- se.exec_start : 266066.098182 se.vruntime : 51893.050177 se.sum_exec_runtime : 2367.077751 se.avg_overlap : 0.077492 nr_switches : 897 nr_voluntary_switches : 828 nr_involuntary_switches : 69 se.load.weight : 1024 policy : 3 prio : 120 clock-delta : 109
> > static void dequeue_task(struct rq *rq, struct task_struct *p, int sleep) > > { > > + u64 limit = sysctl_sched_migration_cost; > > + u64 runtime = p->se.sum_exec_runtime - p->se.prev_sum_exec_runtime; > > + > > if (sleep && p->se.last_wakeup) { > > update_avg(&p->se.avg_overlap, > > p->se.sum_exec_runtime - p->se.last_wakeup); > > p->se.last_wakeup = 0; > > - } > > + } else if (p->se.avg_overlap < limit && runtime >= limit) > > + update_avg(&p->se.avg_overlap, runtime); > > > > sched_info_dequeued(p); > > p->sched_class->dequeue_task(rq, p, sleep); > > hm, that's weird. We want to limit avg_overlap maintenance to > true sleeps only.
Except that when we stop sleeping, we're left with a stale avg_overlap.
> And this patch only makes a difference in the !sleep case - > which shouldnt be that common in this workload.
Hack was only to kill the stale zero. Let's forget hack ;-)
-Mike
| |