On Mon, May 23, 2016 at 05:42:20PM +0200, Mike Galbraith wrote: > On Mon, 2016-05-23 at 15:10 +0100, Morten Rasmussen wrote: > > 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 :-( > > Yup, the goals are pretty much mutually exclusive. For your goal, you > want more of an allocator like behavior, where stacking of tasks is bad > only once there's too much overlap (ie latency, defining is hard), and > allocation always has the same order (expand rightward or such for the > general case, adding little/big complexity for arm). For mine, current > behavior is good, avoid stacking like the plague.
I'd be happy to have a switch to either one goal.
