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SubjectRe: [PATCH RT 5/8] sched/deadline: Reclaim cpuset bandwidth in .migrate_task_rq()
Hi Scott,

On 27/07/19 00:56, Scott Wood wrote:
> With the changes to migrate disabling, ->set_cpus_allowed() no longer
> gets deferred until migrate_enable(). To avoid releasing the bandwidth
> while the task may still be executing on the old CPU, move the subtraction
> to ->migrate_task_rq().
>
> Signed-off-by: Scott Wood <swood@redhat.com>
> ---
> kernel/sched/deadline.c | 67 +++++++++++++++++++++++--------------------------
> 1 file changed, 31 insertions(+), 36 deletions(-)
>
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index c18be51f7608..2f18d0cf1b56 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1606,14 +1606,42 @@ static void yield_task_dl(struct rq *rq)
> return cpu;
> }
>
> +static void free_old_cpuset_bw_dl(struct rq *rq, struct task_struct *p)
> +{
> + struct root_domain *src_rd = rq->rd;
> +
> + /*
> + * Migrating a SCHED_DEADLINE task between exclusive
> + * cpusets (different root_domains) entails a bandwidth
> + * update. We already made space for us in the destination
> + * domain (see cpuset_can_attach()).
> + */
> + if (!cpumask_intersects(src_rd->span, p->cpus_ptr)) {
> + struct dl_bw *src_dl_b;
> +
> + src_dl_b = dl_bw_of(cpu_of(rq));
> + /*
> + * We now free resources of the root_domain we are migrating
> + * off. In the worst case, sched_setattr() may temporary fail
> + * until we complete the update.
> + */
> + raw_spin_lock(&src_dl_b->lock);
> + __dl_sub(src_dl_b, p->dl.dl_bw, dl_bw_cpus(task_cpu(p)));
> + raw_spin_unlock(&src_dl_b->lock);
> + }
> +}
> +
> static void migrate_task_rq_dl(struct task_struct *p, int new_cpu __maybe_unused)
> {
> struct rq *rq;
>
> - if (p->state != TASK_WAKING)
> + rq = task_rq(p);
> +
> + if (p->state != TASK_WAKING) {
> + free_old_cpuset_bw_dl(rq, p);

What happens if a DEADLINE task is moved between cpusets while it was
sleeping? Don't we miss removing from the old cpuset if the task gets
migrated on wakeup?

Thanks,

Juri

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