On 03/26/2013 11:55 PM, Vincent Guittot wrote: >> > So extrapolating that to a 4+4 big-little you'd get something like: >> > >> > | little A9 || big A15 | >> > | 0 | 1 | 2 | 3 || 4 | 5 | 6 | 7 | >> > ------+---+---+---+---++---+---+---+---+ >> > buddy | 0 | 0 | 0 | 0 || 0 | 4 | 4 | 4 | >> > >> > Right? > yes > >> > >> > So supposing the current ILB is 6, we'll only check 4, not 0-3, even >> > though there might be a perfectly idle cpu in there. > We will check 4,5,7 at MC level in order to pack in the group of A15 > (because they are not sharing the same power domain). If none of them > are idle, we will look at CPU level and will check CPUs 0-3.
So you increase a fixed step here. > >> > >> > Also, your scheme fails to pack when cpus 0,4 are filled, even when >> > there's idle cores around. > The primary target is to pack the tasks only when we are in a not busy > system so you will have a power improvement without performance > decrease. is_light_task function returns false and is_buddy_busy > function true before the buddy is fully loaded and the scheduler will > fall back into the default behavior which spreads tasks and races to > idle. > > We can extend the buddy CPU and the packing mechanism to fill one CPU > before filling another buddy but it's not always the best choice for > performance and/or power and thus it will imply to have a knob to > select this full packing mode. Just one buddy to pack tasks for whole level cpus definitely has scalability problem. That is not good for powersaving in most of scenarios. -- Thanks Alex -- 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/
