Hi Vincent,
On Wed, May 13, 2020 at 02:33:35PM +0200 Vincent Guittot wrote:
> enqueue_task_fair jumps to enqueue_throttle label when cfs_rq_of(se) is
> throttled which means that se can't be NULL and we can skip the test.
>
s/be NULL/be non-NULL/
I think.
It's more like if it doesn't jump to the label then se must be NULL for
the loop to terminate. The final loop is a NOP if se is NULL. The check
wasn't protecting that.
Otherwise still
> Reviewed-by: Phil Auld <pa...@redhat.com>
Cheers,
Phil
> Signed-off-by: Vincent Guittot <vincent.guit...@linaro.org>
> ---
>
> v2 changes:
> - Remove useless if statement
>
> kernel/sched/fair.c | 39 ++++++++++++++++++++-------------------
> 1 file changed, 20 insertions(+), 19 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index a0c690d57430..b51b12d63c39 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5513,28 +5513,29 @@ enqueue_task_fair(struct rq *rq, struct task_struct
> *p, int flags)
> list_add_leaf_cfs_rq(cfs_rq);
> }
>
> -enqueue_throttle:
> - if (!se) {
> - add_nr_running(rq, 1);
> - /*
> - * Since new tasks are assigned an initial util_avg equal to
> - * half of the spare capacity of their CPU, tiny tasks have the
> - * ability to cross the overutilized threshold, which will
> - * result in the load balancer ruining all the task placement
> - * done by EAS. As a way to mitigate that effect, do not account
> - * for the first enqueue operation of new tasks during the
> - * overutilized flag detection.
> - *
> - * A better way of solving this problem would be to wait for
> - * the PELT signals of tasks to converge before taking them
> - * into account, but that is not straightforward to implement,
> - * and the following generally works well enough in practice.
> - */
> - if (flags & ENQUEUE_WAKEUP)
> - update_overutilized_status(rq);
> + /* At this point se is NULL and we are at root level*/
> + add_nr_running(rq, 1);
> +
> + /*
> + * Since new tasks are assigned an initial util_avg equal to
> + * half of the spare capacity of their CPU, tiny tasks have the
> + * ability to cross the overutilized threshold, which will
> + * result in the load balancer ruining all the task placement
> + * done by EAS. As a way to mitigate that effect, do not account
> + * for the first enqueue operation of new tasks during the
> + * overutilized flag detection.
> + *
> + * A better way of solving this problem would be to wait for
> + * the PELT signals of tasks to converge before taking them
> + * into account, but that is not straightforward to implement,
> + * and the following generally works well enough in practice.
> + */
> + if (flags & ENQUEUE_WAKEUP)
> + update_overutilized_status(rq);
>
> }
>
> +enqueue_throttle:
> if (cfs_bandwidth_used()) {
> /*
> * When bandwidth control is enabled; the cfs_rq_throttled()
> --
> 2.17.1
>
--
