On Wed, May 11, 2016 at 05:05:50AM +0800, Yuyang Du wrote: > On Mon, May 09, 2016 at 12:48:12PM +0200, Peter Zijlstra wrote: > > + i = select_idle_core(p, sd, target); > > + if ((unsigned)i < nr_cpumask_bits) > > + return i; > > + > > + i = select_idle_cpu(p, sd, target); > > + if ((unsigned)i < nr_cpumask_bits) > > + return i; > > + > > + i = select_idle_smt(p, sd, target); > > + if ((unsigned)i < nr_cpumask_bits) > > + return i; > > First, on smt, these three scans have a lot of overlap,
Limited, we stop doing the idle_core scan the moment we fail to find one. And on a busy system it is unlikely to come back. Which leaves us with the straight idle_cpu scan. Sure, the one time we fail to find an idle core and fall through we'll scan double, but that should be rare. > Then, I am still considering combining them a bit, like the following patch. > And if you want, more might be combined. I tried that (and you really want the last idle it finds, to minimize the time between testing for idle and returning it), but it didn't matter for anything I could find.
