On Mon, May 23, 2016 at 03:00:46PM +0200, Mike Galbraith wrote: > On Mon, 2016-05-23 at 13:00 +0100, Morten Rasmussen wrote: > > > The problem then seems to be distinguishing truly idle and busy doing > > interrupts. The issue that I observe is that wake_wide() likes pushing > > tasks around in lightly scenarios which isn't desirable for power > > management. Selecting the same cpu again may potentially let others > > reach deeper C-state. > > > > With that in mind I will if I can do better. Suggestions are welcome :-) > > None here. For big boxen that are highly idle, you'd likely want to > shut down nodes and consolidate load, but otoh, all that slows response > to burst, which I hate. I prefer race to idle, let power gating do its > job. If I had a server farm with enough capacity vs load variability > to worry about, I suspect I'd become highly interested in routing.
I don't disagree for systems of that scale, but at the other end of the spectrum it is a single SoC we are trying squeeze the best possible mileage out of. That implies optimizing for power gating to reach deeper C-states when possible by consolidating idle-time and grouping idle cpus. Migrating task unnecessarily isn't helping us in achieving that, unfortunately :-(
