On Fri, Aug 28, 2020 at 03:51:13PM -0400, Julien Desfossez wrote:
> /*
> * The static-key + stop-machine variable are needed such that:
> *
> @@ -4641,7 +4656,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev,
> struct rq_flags *rf)
> struct task_struct *next, *max = NULL;
> const struct sched_class *class;
> const struct cpumask *smt_mask;
> - int i, j, cpu;
> + int i, j, cpu, occ = 0;
> int smt_weight;
> bool need_sync;
>
> @@ -4750,6 +4765,9 @@ pick_next_task(struct rq *rq, struct task_struct *prev,
> struct rq_flags *rf)
> goto done;
> }
>
> + if (!is_idle_task(p))
> + occ++;
> +
> rq_i->core_pick = p;
>
> /*
> @@ -4775,6 +4793,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev,
> struct rq_flags *rf)
>
> cpu_rq(j)->core_pick = NULL;
> }
> + occ = 1;
> goto again;
> } else {
> /*
> @@ -4820,6 +4839,8 @@ next_class:;
> if (is_idle_task(rq_i->core_pick) && rq_i->nr_running)
> rq_i->core_forceidle = true;
>
> + rq_i->core_pick->core_occupation = occ;
> +
> if (i == cpu)
> continue;
>
> @@ -4837,6 +4858,113 @@ next_class:;
> return next;
> }
>
> +static bool try_steal_cookie(int this, int that)
> +{
> + struct rq *dst = cpu_rq(this), *src = cpu_rq(that);
> + struct task_struct *p;
> + unsigned long cookie;
> + bool success = false;
> +
> + local_irq_disable();
> + double_rq_lock(dst, src);
> +
> + cookie = dst->core->core_cookie;
> + if (!cookie)
> + goto unlock;
> +
> + if (dst->curr != dst->idle)
> + goto unlock;
> +
> + p = sched_core_find(src, cookie);
> + if (p == src->idle)
> + goto unlock;
> +
> + do {
> + if (p == src->core_pick || p == src->curr)
> + goto next;
> +
> + if (!cpumask_test_cpu(this, &p->cpus_mask))
> + goto next;
> +
> + if (p->core_occupation > dst->idle->core_occupation)
> + goto next;
> +
Can you please explain the rationale behind this check? If I understand
correctly, p->core_occupation is set in pick_next_task() to indicate
the number of matching cookie (except idle) tasks picked on this core.
It is not reset anywhere.
> + p->on_rq = TASK_ON_RQ_MIGRATING;
> + deactivate_task(src, p, 0);
> + set_task_cpu(p, this);
> + activate_task(dst, p, 0);
> + p->on_rq = TASK_ON_RQ_QUEUED;
> +
> + resched_curr(dst);
> +
> + success = true;
> + break;
> +
> +next:
> + p = sched_core_next(p, cookie);
> + } while (p);
> +
> +unlock:
> + double_rq_unlock(dst, src);
> + local_irq_enable();
> +
> + return success;
> +}
Thanks,
Pavan
--
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Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux
Foundation Collaborative Project.
