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sched/fair: Don't set LBF_ALL_PINNED unnecessarily 

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.

LBF_ALL_PINNED flag is now always set it by default. It is then cleared
when we find one task that can be pulled when calling detach_tasks() or
during active migration.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Link: https://lkml.kernel.org/r/20210107103325.30851-3-vincent.guittot@linaro.org
This commit is contained in:
Vincent Guittot 2021-01-07 11:33:24 +01:00 committed by Peter Zijlstra
parent fc488ffd42
commit 8a41dfcda7
1 changed files with 5 additions and 2 deletions
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7
kernel/sched/fair.c
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@ -9639,6 +9639,8 @@ static int load_balance(int this_cpu, struct rq *this_rq,
env.src_rq = busiest;
ld_moved = 0;
/* Clear this flag as soon as we find a pullable task */
env.flags |= LBF_ALL_PINNED;
if (busiest->nr_running > 1) {
/*
* Attempt to move tasks. If find_busiest_group has found
@ -9646,7 +9648,6 @@ 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:
@ -9772,10 +9773,12 @@ 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;
}
/* Record that we found at least one task that could run on this_cpu */
env.flags &= ~LBF_ALL_PINNED;
/*
* ->active_balance synchronizes accesses to
* ->active_balance_work. Once set, it's cleared