On Wed, Jan 06, 2021 at 02:34:18PM +0100, Vincent Guittot wrote: > Setting LBF_ALL_PINNED during active load balance is only valid when there > is only 1 running task on the rq otherwise this ends up increasing the > balance interval whereas other tasks could migrate after the next interval > once they become cache-cold as an example. > > Signed-off-by: Vincent Guittot <[email protected]> > --- > kernel/sched/fair.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 5428b8723e61..69a455113b10 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -9759,7 +9759,8 @@ static int load_balance(int this_cpu, struct rq > *this_rq, > if (!cpumask_test_cpu(this_cpu, > busiest->curr->cpus_ptr)) { > raw_spin_unlock_irqrestore(&busiest->lock, > flags); > - env.flags |= LBF_ALL_PINNED; > + if (busiest->nr_running == 1) > + env.flags |= LBF_ALL_PINNED; > goto out_one_pinned; > }
Hmm.. that wasn't the intention. It's entirely possible to have multiple tasks pinned. ISTR we set all-pinned and then clear it in can_migrate_task() when we actually find a task that can be moved to the destination CPU. That's a construct that works perfectly fine with multiple tasks.
