On Fri, Jul 03, 2015 at 06:38:31PM +0200, Peter Zijlstra wrote: > > I'm not against having a policy that sits somewhere in between, we just > > have to agree it is the right policy and clean up the load-balance code > > such that the implemented policy is clear. > > Right, for balancing its a tricky question, but mixing them without > intent is, as you say, a bit of a mess. > > So clearly blocked load doesn't make sense for (new)idle balancing. OTOH > it does make some sense for the regular periodic balancing, because > there we really do care mostly about the averages, esp. so when we're > overloaded -- but there are issues there too. > > Now we can't track them both (or rather we could, but overhead). > > I like Yuyang's load tracking rewrite, but it changes exactly this part, > and I'm not sure I understand the full ramifications of that yet. Thanks. It would be a pure average policy, which is non-perfect like now, and certainly needs a mixing like now, but it is worth a starter, because it is simple and reasaonble, and based on it, the other parts can be simple and reasonable.
> One way out would be to split the load balancer into 3 distinct regions; > > 1) get a task on every CPU, screw everything else. > 2) get each CPU fully utilized, still ignoring 'load' > 3) when everybody is fully utilized, consider load. > > If we make find_busiest_foo() select one of these 3, and make > calculate_imbalance() invariant to the metric passed in, and have things > like cpu_load() and task_load() return different, but coherent, numbers > depending on which region we're in, this almost sounds 'simple'. > > The devil is in the details, and the balancer is a hairy nest of details > which will make the above non-trivial. > > But for 1) we could simply 'balance' on nr_running, for 2) we can > 'balance' on runnable_avg and for 3) we'll 'balance' on load_avg (which > will then include blocked load). > > Let me go play outside for a bit so that it can sink in what kind of > nonsense my heat addled brain has just sprouted :-) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
