Messages in this thread | | | Date | Thu, 11 Sep 2003 21:04:45 +1000 | From | Nick Piggin <> | Subject | Re: [PATCH] Minor scheduler fix to get rid of skipping in xmms |
| |
Andrew Theurer wrote:
>Robert Love <rml@tech9.net> wrote: > >>> There are a _lot_ of scheduler changes in 2.6-mm, and who knows which >>> ones are an improvement, a detriment, and a noop? >>> > >>We know that sched-2.6.0-test2-mm2-A3.patch caused the regression, and >>we now that sched-CAN_MIGRATE_TASK-fix.patch mostly fixed it up. >> > >>What we don't know is whether the thing which >>sched-CAN_MIGRATE_TASK-fix.patch >>fixed was the thing which sched-2.6.0-test2-mm2-A3.patch broke. >> > >Sorry for jumping into this late. I didn't even know the can_migrate patch >was being discussed, let alone in -mm :). And to be fair, this really is >Ingo's aggressive idle steal patch. > >Anyway, these patches are somewhat related. It would seem that A3's >shortening the tasks' run time would not only slow performance beacuse of >cache thrash, but could possibly break CAN_MIGRATE's cache warmth check, >right? That in turn would stop load balancing from working well, leading to >more idle time, which the CAN_MIGRATE patch sort of bypassed for idle cpus. >
Yeah thats probably right. Good thinking.
> >I see Nick's balance patch as somewhat harmless, at least combined with A3 >patch. However, one concern is that the "ping-pong" steal interval is not >really 200ms, but 200ms/(nr_cpus-1), which without A3, could show up as a >problem, especially on an 8 way box. In addition, I do think there's a >problem with num tasks we steal. It should not be imbalance/2, it should be: >max_load - (node_nr_running / num_cpus_node). If we steal any more than >this, which is quite possible with imbalance/2, then it's likely this_cpu now >has too many tasks, and some other cpu will steal again. Using *imbalance/2 >works fine on 2-way smp, but I'm pretty sure we "over steal" tasks on 4 way >and up. Anyway, I'm getting off topic here... >
IIRC max_load is supposed to be the number of tasks on the runqueue being stolen from, isn't it?
- 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/
| |