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SubjectRe: [PATCH V3 1/2] sched/fair: Fix load_balance() affinity redo path
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On 18/05/17 20:36, Jeffrey Hugo wrote:

[...]

> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index d711093..a5d41b1 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8220,7 +8220,24 @@ static int load_balance(int this_cpu, struct rq *this_rq,
> /* 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)) {
> + /*
> + * dst_cpu is not a valid busiest cpu in the following
> + * check since load cannot be pulled from dst_cpu to be
> + * put on dst_cpu.
> + */
> + cpumask_clear_cpu(env.dst_cpu, cpus);
> + /*
> + * Go back to "redo" iff the load-balance cpumask
> + * contains other potential busiest cpus for the
> + * current sched domain.
> + */
> + if (cpumask_intersects(cpus, sched_domain_span(env.sd))) {
> + /*
> + * Now that the check has passed, reenable
> + * dst_cpu so that load can be calculated on
> + * it in the redo path.
> + */
> + cpumask_set_cpu(env.dst_cpu, cpus);

IMHO, this will work nicely and its way easier.

Another idea might be to check if the LBF_ALL_PINNED is set when we
check if we should clean the imbalance flag.

@@ -8307,14 +8307,13 @@ static int load_balance(int this_cpu, struct rq *this_rq,
* We reach balance although we may have faced some affinity
* constraints. 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;
}

But I think preventing a needless redo loop is even better ...

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