Ping Peter
> From: Xunlei Pang <pang.xun...@linaro.org>
>
> In load_balance(), some members of lb_env will be assigned with
> new values in LBF_DST_PINNED case. But lb_env::flags may still
> retain LBF_ALL_PINNED if no proper tasks were found afterwards
> due to another balance, task affinity changing, etc, which can
> really happen because busiest rq lock has already been released.
>
> This is wrong, for example with env.dst_cpu assigned new_dst_cpu
> when going back to "redo" label, it may cause should_we_balance()
> to return false which is unreasonable.
>
> This patch restores proper status of env before "goto redo", and
> improves "out_all_pinned" and "out_one_pinned" labels.
>
> Signed-off-by: Xunlei Pang <pang.xun...@linaro.org>
> ---
> kernel/sched/fair.c | 35 ++++++++++++++++++++---------------
> 1 file changed, 20 insertions(+), 15 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index ee595ef..45bbda1 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6843,6 +6843,7 @@ static int load_balance(int this_cpu, struct rq
> *this_rq,
> .dst_cpu = this_cpu,
> .dst_rq = this_rq,
> .dst_grpmask = sched_group_cpus(sd->groups),
> + .new_dst_cpu = -1,
> .idle = idle,
> .loop_break = sched_nr_migrate_break,
> .cpus = cpus,
> @@ -6977,12 +6978,19 @@ more_balance:
> /* All tasks on this runqueue were pinned by CPU affinity */
> if (unlikely(env.flags & LBF_ALL_PINNED)) {
> cpumask_clear_cpu(cpu_of(busiest), cpus);
> - if (!cpumask_empty(cpus)) {
> - env.loop = 0;
> - env.loop_break = sched_nr_migrate_break;
> - goto redo;
> + if (env.new_dst_cpu != -1) {
> + env.new_dst_cpu = -1;
> + cpumask_or(cpus, cpus,
> + sched_group_cpus(sd->groups));
> + cpumask_and(cpus, cpus, cpu_active_mask);
> +
> + env.dst_cpu = this_cpu;
> + env.dst_rq = this_rq;
> }
> - goto out_all_pinned;
> + env.flags &= ~LBF_SOME_PINNED;
> + env.loop = 0;
> + env.loop_break = sched_nr_migrate_break;
> + goto redo;
> }
> }
>
> @@ -7009,7 +7017,7 @@ more_balance:
> raw_spin_unlock_irqrestore(&busiest->lock,
> flags);
> env.flags |= LBF_ALL_PINNED;
> - goto out_one_pinned;
> + goto out_active_balanced;
> }
>
> /*
> @@ -7058,26 +7066,23 @@ more_balance:
> out_balanced:
> /*
> * We reach balance although we may have faced some affinity
> - * constraints. Clear the imbalance flag if it was set.
> + * constraints.
> + *
> + * When LBF_ALL_PINNED was not set, clear the imbalance flag
> + * if it was set.
> */
> - if (sd_parent) {
> + if (sd_parent && !(env.flags & LBF_ALL_PINNED)) {
> int *group_imbalance = &sd_parent->groups->sgc->imbalance;
>
> if (*group_imbalance)
> *group_imbalance = 0;
> }
>
> -out_all_pinned:
> - /*
> - * We reach balance because all tasks are pinned at this level so
> - * we can't migrate them. Let the imbalance flag set so parent level
> - * can try to migrate them.
> - */
> schedstat_inc(sd, lb_balanced[idle]);
>
> sd->nr_balance_failed = 0;
>
> -out_one_pinned:
> +out_active_balanced:
> /* tune up the balancing interval */
> if (((env.flags & LBF_ALL_PINNED) &&
> sd->balance_interval < MAX_PINNED_INTERVAL) ||
> --
> 1.9.1
>
>
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