On Tue, Mar 08, 2005 at 07:17:31PM +1100, Nick Piggin wrote: > Siddha, Suresh B wrote: > > That still might not be enough. We probably need to pass push_cpu's > > sd to move_tasks call in active_load_balance, instead of current > > busiest_cpu's > > sd. Just like push_cpu, we need to add one more field to the runqueue which > > will specify the domain level of the push_cpu at which we have an imbalance. > > > > It should be the lowest domain level that spans both this_cpu and > push_cpu, and has the SD_BALANCE flag set. We could possibly be a bit
I agree. > more general here, but so long as nobody is coming up with weird and > wonderful sched_domains schemes, push_cpu should give you all the info > needed. > > > push_cpu might not be the ideal destination in all cases. Take a NUMA domain > > above SMT+SMP domains in my above example. Assume P0, P1 is in node-0 and > > P2, P3 in node-1. Assume Loads of P0,P1,P2 are same as the above > > example,with P3 > > containing one process load. Now any idle thread in P2 or P3 can trigger > > active load balance on P0. We should be selecting thread in P2 ideally > > (currently this is what we get with idle package check). But with push_cpu, > > we might move to the idle thread in P3 and then finally move to P2(it will > > be a > > two step process) > > > > Hmm yeah. It is a bit tricky. We don't currently do exceptionally well > at this sort of "balancing over multiple domains" very well in the > periodic balancer either. With periodic balancer, moved tasks will not be actively running and by the time it gets a cpu slot, it will most probably be on the correct cpu (though "most probably" is the key word here ;-) > But at this stage I prefer to not get overly complex, and allow some > imperfect task movement, because it should rarely be a problem, and is > much better than it was before. The main place where it can go wrong > is multi-level NUMA balancing, where moving a task twice (between > different nodes) can cause more problems. With active_load_balance, we will be moving the currently running process. So obviously if we can move in one single step, that will be nice. I agree with the complexity part though. And it will become more complex with upcoming dual-core requirements. thanks, suresh - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
