On Fri, 2013-03-22 at 13:25 +0100, Vincent Guittot wrote: > During the creation of sched_domain, we define a pack buddy CPU for > each CPU > when one is available. We want to pack at all levels where a group of > CPU can > be power gated independently from others. > On a system that can't power gate a group of CPUs independently, the > flag is > set at all sched_domain level and the buddy is set to -1. This is the > default > behavior. > On a dual clusters / dual cores system which can power gate each core > and > cluster independently, the buddy configuration will be : > > | Cluster 0 | Cluster 1 | > | CPU0 | CPU1 | CPU2 | CPU3 | > ----------------------------------- > buddy | CPU0 | CPU0 | CPU0 | CPU2 |
I suppose this is adequate for the 'small' systems you currently have; but given that Samsung is already bragging with its 'octo'-core Exynos 5 (4+4 big-little thing) does this solution scale? Isn't this basically related to picking the NO_HZ cpu; if the system isn't fully symmetric with its power gates you want the NO_HZ cpu to be the 'special' cpu. If it is symmetric we really don't care which core is left 'running' and we can even select a new pack cpu from the idle cores once the old one is fully utilized. Re-using (or integrating) with NO_HZ has the dual advantage that you'll make NO_HZ do the right thing for big-little (you typically want a little core to be the one staying 'awake' and once someone makes NO_HZ scale this all gets to scale along with it. -- 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/
