On Fri, Jun 01, 2018 at 04:10:56PM +0900, Byungchul Park wrote:
> > On Thu, May 31, 2018 at 11:12:55PM -0700, Joel Fernandes wrote:
> > > On Mon, Jan 08, 2018 at 03:14:41PM +0900, byungchul park wrote:
> > > > Currently, migrating tasks to cpu0 unconditionally happens when the
> > > > heap is empty, since cp->elements[].cpu was initialized to 0(=cpu0).
> > > > We have to distinguish between the empty case and cpu0 to avoid the
> > > > unnecessary migrations. Therefore, it has to return an invalid value
> > > > e.i. -1 in that case.
> > > >
> > > > Signed-off-by: Byungchul Park <[email protected]>
> > > > Acked-by: Steven Rostedt (VMware) <[email protected]>
> > > > Acked-by: Daniel Bristot de Oliveira <[email protected]>
> > > > ---
> > > > kernel/sched/cpudeadline.c | 10 +++++++++-
> > > > 1 file changed, 9 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
> > > > index 9f02035..bcf903f 100644
> > > > --- a/kernel/sched/cpudeadline.c
> > > > +++ b/kernel/sched/cpudeadline.c
> > > > @@ -138,6 +138,12 @@ int cpudl_find(struct cpudl *cp, struct
> > > > task_struct *p,
> > > > int best_cpu = cpudl_maximum_cpu(cp);
> > > > WARN_ON(best_cpu != -1 && !cpu_present(best_cpu));
> > > > + /*
> > > > + * The heap tree is empty for now, just return.
> > > > + */
> > > > + if (best_cpu == -1)
> > > > + return 0;
> > > > +
> > > > if (cpumask_test_cpu(best_cpu, &p->cpus_allowed) &&
> > > > dl_time_before(dl_se->deadline,
> > > > cpudl_maximum_dl(cp))) {
> > > > if (later_mask)
> > > > @@ -265,8 +271,10 @@ int cpudl_init(struct cpudl *cp)
> > > > return -ENOMEM;
> > > > }
> > > > - for_each_possible_cpu(i)
> > > > + for_each_possible_cpu(i) {
> > > > + cp->elements[i].cpu = -1;
> > > > cp->elements[i].idx = IDX_INVALID;
> > >
> > > Shouldn't you also set cp->elements[cpu].cpu to -1 in cpudl_clear (when
> > > you
> > > set cp->elements[cpu].cpu to IDX_INVALID there)?
> >
> > I messed up my words, I meant : "when setting cp->elements[cpu].idx to
> > IDX_INVALID there". Which means I need to call it a day :-)
>
> Ah.. I agree with you. It might be a problem when removing the last
> element.. Then I think the following change should also be applied
> additionally. Right?
Yes.
> ---
> diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
> index 8d9562d..44d4c88 100644
> --- a/kernel/sched/cpudeadline.c
> +++ b/kernel/sched/cpudeadline.c
> @@ -172,12 +172,14 @@ void cpudl_clear(struct cpudl *cp, int cpu)
> } else {
> new_cpu = cp->elements[cp->size - 1].cpu;
> cp->elements[old_idx].dl = cp->elements[cp->size - 1].dl;
> - cp->elements[old_idx].cpu = new_cpu;
> + cp->elements[old_idx].cpu = (new_cpu == cpu) ? -1 : new_cpu;
> cp->size--;
> - cp->elements[new_cpu].idx = old_idx;
> cp->elements[cpu].idx = IDX_INVALID;
> - cpudl_heapify(cp, old_idx);
>
> + if (new_cpu != cpu) {
> + cp->elements[new_cpu].idx = old_idx;
> + cpudl_heapify(cp, old_idx);
> + }
> cpumask_set_cpu(cpu, cp->free_cpus);
This looks a bit confusing. How about the following? (untested)
thanks,
- Joel
---8<-----------------------
diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
index 50316455ea66..741a97e58c05 100644
--- a/kernel/sched/cpudeadline.c
+++ b/kernel/sched/cpudeadline.c
@@ -129,6 +129,10 @@ int cpudl_find(struct cpudl *cp, struct task_struct *p,
} else {
int best_cpu = cpudl_maximum(cp);
+ /* The max-heap is empty, just return. */
+ if (best_cpu == -1)
+ return 0;
+
WARN_ON(best_cpu != -1 && !cpu_present(best_cpu));
if (cpumask_test_cpu(best_cpu, &p->cpus_allowed) &&
@@ -167,6 +171,12 @@ void cpudl_clear(struct cpudl *cp, int cpu)
* This could happen if a rq_offline_dl is
* called for a CPU without -dl tasks running.
*/
+ } else if (cp->size == 1) {
+ /* Only one element in max-heap, clear it */
+ cp->elements[0].cpu = -1;
+ cp->elements[cpu].idx = IDX_INVALID;
+ cp->size--;
+ cpumask_set_cpu(cpu, cp->free_cpus);
} else {
new_cpu = cp->elements[cp->size - 1].cpu;
cp->elements[old_idx].dl = cp->elements[cp->size - 1].dl;
@@ -262,6 +272,9 @@ int cpudl_init(struct cpudl *cp)
for_each_possible_cpu(i)
cp->elements[i].idx = IDX_INVALID;
+ /* Mark heap as initially empty */
+ cp->elements[0].cpu = -1;
+
return 0;
}
