On Thu, Apr 12, 2018 at 08:22:11PM +0200, Peter Zijlstra wrote: > On Tue, Apr 10, 2018 at 02:19:50PM +0100, Morten Rasmussen wrote: > > As said above, I see your point about completion time might suffer in > > some cases for low utilization tasks, but I don't see how you can fix > > that automagically. ASYM_PACKING has a lot of problematic side-effects. > > If use-space knows that completion time is important for a task, there > > are already ways to improve that somewhat in mainline (task priority and > > pinning), and more powerful solutions in the Android kernel which > > Patrick is currently pushing upstream. > > So I tend to side with Morten on this one. I don't particularly like > ASYM_PACKING much, but we already had it for PPC and it works for the > small difference in performance ITMI has. > > At the time Morten already objected to using it for ITMI, and I just > haven't had time to look into his proposal for using capacity. > > But I don't see it working right for big.litte/dynamiq, simply because > it is a very strong always big preference, which is against the whole > design premisis of big.little (as Morten has been trying to argue).
In Vincent's defence, vendors do sometimes make design decisions that I don't quite understand. So there could be users that really want a non-energy-aware big-first policy, but as I said earlier in this thread, that could be implemented better with a small tweak to wake_cap() and using the misfit patches. We would have to disable big-first policy and go with the current migrate-big-task-to-big-cpus policy as soon as we care about energy. I'm happy to give that try and come up with a patch.
