On Tue, Jun 06, 2017 at 02:30:11PM +0200, Peter Zijlstra wrote: > So with that the problem is that active_load_balance_cpu_stop() calls > into can_migrate_task() with ->idle = CPU_IDLE and !dst_grpmask, which > then goes *bang*. Now active_load_balance_cpu_stop() doesn't need to > re-evaluate anything, so ideally it would just skip this entirely, > right? > > So why not do #3: > > --- > kernel/sched/fair.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 47a0c552c77b..fd639d32fa4c 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -8523,6 +8523,13 @@ static int active_load_balance_cpu_stop(void *data) > .src_cpu = busiest_rq->cpu, > .src_rq = busiest_rq, > .idle = CPU_IDLE,
So I realized that setting CPU_NEW_IDLE here does the 'same' thing. Except that would be a 'visible' change in the schedstat output (not sure anybody really cares about that). > + /* > + * can_migrate_task() doesn't need to compute > new_dst_cpu > + * for active balancing. Since we have CPU_IDLE, but no > + * @dst_grpmask we need to make that test go away with > lying > + * about DST_PINNED. > + */ > + .flags = LBF_DST_PINNED, But given this is trivial and doesn't have any visible side effects, this seems 'better'. > }; > > schedstat_inc(sd->alb_count);
