On Mon, 2016-05-23 at 11:58 +0100, Morten Rasmussen wrote: > wake_wide() is based on task wakee_flips of the waker and the wakee to > decide whether an affine wakeup is desirable. On lightly loaded systems > the waker is frequently the idle task (pid=0) which can accumulate a lot > of wakee_flips in that scenario. It makes little sense to prevent affine > wakeups on an idle cpu due to the idle task wakee_flips, so it makes > more sense to ignore them in wake_wide().
You sure? What's the difference between a task flipping enough to warrant spreading the load, and an interrupt source doing the same? I've both witnessed firsthand, and received user confirmation of this very thing improving utilization. > cc: Ingo Molnar <mi...@redhat.com> > cc: Peter Zijlstra <pet...@infradead.org> > > Signed-off-by: Morten Rasmussen <morten.rasmus...@arm.com> > --- > kernel/sched/fair.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index c49e25a..0fe3020 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -5007,6 +5007,10 @@ static int wake_wide(struct task_struct *p) > unsigned int slave = p->wakee_flips; > int factor = this_cpu_read(sd_llc_size); > > + /* Don't let the idle task prevent affine wakeups */ > + if (is_idle_task(current)) > + return 0; > + > if (master < slave) > swap(master, slave); > if (slave < factor || master < slave * factor)
