Re: [RESEND, v3, 2/2] sched/deadline: Initialize cp->elements[].cpu to an invalid value
From: Byungchul Park
Date: Fri Jun 01 2018 - 03:11:06 EST
On 2018-06-01 15:18, Joel Fernandes 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 <byungchul.park@xxxxxxx>
Acked-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Acked-by: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
---
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?
---
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);
}
raw_spin_unlock_irqrestore(&cp->lock, flags);
--
Thanks,
Byungchul