Messages in this thread | | | Date | Wed, 13 May 2020 08:45:40 -0400 | From | Phil Auld <> | Subject | Re: [PATCH v2] sched/fair: enqueue_task_fair optimization |
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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 <pauld@redhat.com>
Cheers, Phil
> Signed-off-by: Vincent Guittot <vincent.guittot@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 >
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