Messages in this thread Patch in this message | | | From | Valentin Schneider <> | Subject | Re: [PATCH 2/3] sched/fair: don't set LBF_ALL_PINNED unnecessarily | Date | Wed, 06 Jan 2021 15:13:47 +0000 |
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On 06/01/21 14:34, 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 <vincent.guittot@linaro.org> > --- > 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;
So LBF_ALL_PINNED *can* be set if busiest->nr_running > 1, because before we get there we have:
if (nr_running > 1) { env.flags |= LBF_ALL_PINNED; detach_tasks(&env); // Removes LBF_ALL_PINNED if > 0 tasks can be pulled ... }
What about following the logic used by detach_tasks() and only clear the flag? Say something like the below. if nr_running > 1, then we'll have gone through detach_tasks() and will have cleared the flag (if possible). --- diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 04a3ce20da67..211c86ba3f5b 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -9623,6 +9623,8 @@ static int load_balance(int this_cpu, struct rq *this_rq, env.src_rq = busiest; ld_moved = 0; + /* Clear this as soon as we find a single pullable task */ + env.flags |= LBF_ALL_PINNED; if (busiest->nr_running > 1) { /* * Attempt to move tasks. If find_busiest_group has found @@ -9630,7 +9632,6 @@ static int load_balance(int this_cpu, struct rq *this_rq, * still unbalanced. ld_moved simply stays zero, so it is * correctly treated as an imbalance. */ - env.flags |= LBF_ALL_PINNED; env.loop_max = min(sysctl_sched_nr_migrate, busiest->nr_running); more_balance: @@ -9756,10 +9757,11 @@ 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; goto out_one_pinned; } + env.flags &= ~LBF_ALL_PINNED; + /* * ->active_balance synchronizes accesses to * ->active_balance_work. Once set, it's cleared ---
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