On Mon, 2019-09-30 at 09:12 +0200, Juri Lelli wrote:
> On 27/09/19 11:40, Scott Wood wrote:
> > On Fri, 2019-09-27 at 10:11 +0200, Juri Lelli wrote:
> > > 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@xxxxxxxxxx>
> > > > ---
> > > > 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?
> >
> > In that case set_task_cpu() is called by ttwu after setting state to
> > TASK_WAKING.
>
> Right.
>
> > I guess it could be annoying if the task doesn't wake up for a
> > long time and therefore doesn't release the bandwidth until then.
>
> Hummm, I was actually more worried about the fact that we call free_old_
> cpuset_bw_dl() only if p->state != TASK_WAKING.
Oh, right. :-P Not sure what I had in mind there; we want to call it
regardless.
I assume we need rq->lock in free_old_cpuset_bw_dl()? So something like
this:
if (p->state == TASK_WAITING)
raw_spin_lock(&rq->lock);
free_old_cpuset_bw_dl(rq, p);
if (p->state != TASK_WAITING)
return;
if (p->dl.dl_non_contending) {
....
BTW, is the full cpumask_intersects() necessary or would it suffice to see
that the new cpu is not in the old span?
-Scott
