Messages in this thread | | | Date | Wed, 13 May 2020 09:31:22 -0400 | From | Phil Auld <> | Subject | Re: [PATCH v2] sched/fair: enqueue_task_fair optimization |
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On Wed, May 13, 2020 at 03:25:29PM +0200 Vincent Guittot wrote: > On Wed, 13 May 2020 at 15:18, Phil Auld <pauld@redhat.com> wrote: > > > > On Wed, May 13, 2020 at 03:15:53PM +0200 Vincent Guittot wrote: > > > On Wed, 13 May 2020 at 15:13, Phil Auld <pauld@redhat.com> wrote: > > > > > > > > On Wed, May 13, 2020 at 03:10:28PM +0200 Vincent Guittot wrote: > > > > > On Wed, 13 May 2020 at 14:45, Phil Auld <pauld@redhat.com> wrote: > > > > > > > > > > > > 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. > > > > > > > > > > This sentence refers to the move of enqueue_throttle and the fact that > > > > > se can't be null when goto enqueue_throttle and we can jump directly > > > > > after the if statement, which is now removed in v2 because se is > > > > > always NULL if we don't use goto enqueue_throttle. > > > > > > > > > > I haven't change the commit message for the remove of if statement > > > > > > > > > > > > > Fair enough, it just seems backwards from the intent of the patch now. > > > > > > > > There is also an extra } after the update_overutilized_status. > > > > > > don't know what I did but it's crap. sorry about that > > > > > > > No worries. I didn't see it when I read it either. The compiler told me :) > > Yeah, but i thought that i compiled it which is obviously not true >
It's that "obviously" correct stuff that bites you every time ;)
> > > > > > > Let me prepare a v3 > > > > > > > > > > > > > > > Cheers, > > > > Phil > > > > > > > > > > > > > > > > > > > > > > > > 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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