Messages in this thread | | | Subject | Re: [RFC] sched: Limit idle_balance() when it is being used too frequently | From | Jason Low <> | Date | Thu, 18 Jul 2013 12:03:47 -0700 |
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On Thu, 2013-07-18 at 17:42 +0530, Srikar Dronamraju wrote: > > > > > > idle_balance(u64 idle_duration) > > > { > > > u64 cost = 0; > > > > > > for_each_domain(sd) { > > > if (cost + sd->cost > idle_duration/N) > > > break; > > > > > > ... > > > > > > sd->cost = (sd->cost + this_cost) / 2; > > > cost += this_cost; > > > } > > > } > > > > > > I would've initially suggested using something like N=2 since we're dealing > > > with averages and half should ensure we don't run over except for the worst > > > peaks. But we could easily use a bigger N. > > > > I ran a few AIM7 workloads for the 8 socket HT enabled case and I needed > > to set N to more than 20 in order to get the big performance gains. > > > > As per your observation, newly idle balancing isn't picking tasks and > mostly finding the domains to be balanced. find_busiest_queue() is > under rcu. So where and how are we getting these performance gains?
I actually just ran fserver on 8 sockets (which idle balance lowers the performance in this workload at this socket count), and for this workload, idle balancing is finding tasks to move fairly often on a per-cpu basis. So I guess it is not always the case that idle balancing isn't moving tasks on this box.
Jason
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