On Mon, May 09, 2016 at 11:39:05AM +0200, Mike Galbraith wrote: > On Mon, 2016-05-09 at 09:13 +0800, Yuyang Du wrote: > > On Mon, May 09, 2016 at 09:44:13AM +0200, Mike Galbraith wrote: > > > > In a perfect world, running only Chris' benchmark on an otherwise idle > > > box, there would never _be_ any work to steal. > > > > What is the perfect world like? I don't get what you mean. > > In a perfect world from this benchmark's perspective, when you fork or > wake while box is underutilized, wakee/child lands on an idle CPU. To > this benchmark, anything else is broken. > > > > In the real world, we > > > smooth utilization, optimistically peek at this/that, and intentionally > > > throttle idle balancing (etc etc), which adds up to an imperfect world > > > for this (based on real world load) benchmark. > > > > So, is this a shout-out: these parts should be coordinated better? > > Switching to instantaneous load along with the cpu reservation hackery > made Chris's benchmark a happy camper. Is that the answer? Nope, just > verification of the where the problem lives.
By cpu reservation, you mean the various averages in select_task_rq_fair? It does seem a lot of cleanup should be done. > > > > En... should we try remove recording last_wakee? > > > > > > The more the merrier, go for it! :) > > > > Nuh, really, this heuristic is too heuristic, :) > > The totality of all possible cases is scary. > > Well, make it better. The author provided evidence when it was born. I have to think this through, hot-potato. Maybe even droping it does not sound outrageous.
