Messages in this thread | | | Date | Wed, 11 Nov 2009 18:59:28 +0900 | From | Yasunori Goto <> | Subject | Re: [BUG] cpu controller can't provide fair CPU time for each group |
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After receiving your mail, I realized I misunderstood about test case 1). I thought 1) was occur without cpu affinity due to mis-communication with test team. I'm really really sorry for noise. I need much coffee. :-(
> On Wed, 2009-11-11 at 15:21 +0900, Yasunori Goto wrote: > > > When users use cpuset/cpu affinity, then they would like to controll cpu affinity. > > Not CPU time. > > What are people using affinity for? The only use of affinity is to > restrict or disable the load-balancer. Don't complain the load-balancer > doesn't work when you're taking active steps to hinder its work. > > If you don't want things load-balanced, turn it off, if you want the > load-balancer to work on smaller groups of cpus, use cpusets.
Ok. make sense.
> > Anyway, I said there needs to be done something because the interaction > between cpusets and the cpu-controller is utter crap, they never should > have been separated like they are.
Thanks.
> > > To be honest, I don't have any good idea because I'm not familiar with > > schduler's code. But I have one question. > > > > > > 1618 static int tg_shares_up(struct task_group *tg, void *data) > > 1619 { > > 1620 unsigned long weight, rq_weight = 0, shares = 0; > > > > (snip) > > > > 1632 for_each_cpu(i, sched_domain_span(sd)) { > > 1633 weight = tg->cfs_rq[i]->load.weight; > > 1634 usd->rq_weight[i] = weight; > > 1635 > > 1636 /* > > 1637 * If there are currently no tasks on the cpu pretend there > > 1638 * is one of average load so that when a new task gets to > > 1639 * run here it will not get delayed by group starvation. > > 1640 */ > > 1641 if (!weight) > > 1642 weight = NICE_0_LOAD; ---------(*) > > > > I heard from test team when (*) was removed, 1) didn't occur. > > > > The comment said (*) is to avoid starvation condition. > > However, I don't understand why NICE_0_LOAD must be specified. > > Could you tell me why small value (like 2 or 3) is not used for (*)? > > What is side effect? > > Exactly what the comment says, it will get delayed because the group > won't get scheduled on that cpu until all the group weights get > re-adjusted again, which can be much longer than the typical runtimes of > the workload in question. > > Regular weights are NICE_0_LOAD, if you stick a 3 next to that I'll not > get ran much -> starvation.
Ok.
Thank you very much for your explanation.
Best Regards.
-- Yasunori Goto
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