Messages in this thread |  | | Date | Tue, 28 Mar 2006 11:25:21 -0800 | From | "Siddha, Suresh B" <> | Subject | Re: [PATCH] sched: smpnice work around for active_load_balance() |
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On Tue, Mar 28, 2006 at 05:00:50PM +1100, Peter Williams wrote: > Problem: > > It is undesirable for HT/MC packages to have more than one of their CPUs > busy if there are other packages that have all of their CPUs idle. This
We need to balance even if the other packages are not idle.. For example, consider a 4-core DP system, if we have 6 runnable(assume same priority) processes, we want to schedule 3 of them in each package..
Todays active load balance implementation is very simple and generic. And hence it works smoothly with dual and multi-core.. Please read my OLS 2005 paper which talks about different scheduling scenarios and also how we were planning to implement Power savings policy incase of multi-core.. I had a prototype patch for doing this, which I held it up before going on vacation, as it needed some rework with your smpnice patch in place.. I will post a patch ontop of current mainline for your reference.
> + } else if (!busiest_has_loaded_cpus && avg_load < max_load) {
I haven't fully digested the result of this patch but should this be avg_load < max_load or avg_load > max_load ?
Either way, I can show scheduling scenarios which will fail...
> > - if (rqi->raw_weighted_load > max_load && rqi->nr_running > 1) { > + if (rqi->nr_running > 1) { > + if (rqi->raw_weighted_load > max_load || !busiest_is_loaded) { > + max_load = rqi->raw_weighted_load; > + busiest = rqi; > + busiest_is_loaded = 1; > + } > + } else if (!busiest_is_loaded && rqi->raw_weighted_load > max_load) {
Please note the point that same scheduling logic has to work for all the different levels of scheduler domains... I think these checks complicates the decisions as we go up in the scheduling hirerachy.. Please go through the HT/MC/MP/Numa combinations and with same/different priority processes for different scenarios..
Even with no HT and MC, this patch has still has issues in the presence of different priority tasks... consider a simple DP system and run two instances of high priority tasks(simple infinite loop) and two normal priority tasks. With "top" I observed that these normal priority tasks keep on jumping from one processor to another... Ideally with smpnice, we would assume that each processor should have two tasks (one high priority and another one with normal priority) ..
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