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authorLuca Abeni <luca.abeni@santannapisa.it>2020-05-20 15:42:43 +0200
committerPeter Zijlstra <peterz@infradead.org>2020-06-15 14:10:05 +0200
commit23e71d8ba42933bff12e453858fd68c073bc5258 (patch)
tree204503b03f477b61128e684b39a8e54a69bce97d
parentb4118988fdcb4554ea6687dd8ff68bcab690b8ea (diff)
sched/deadline: Implement fallback mechanism for !fit case
When a task has a runtime that cannot be served within the scheduling deadline by any of the idle CPU (later_mask) the task is doomed to miss its deadline. This can happen since the SCHED_DEADLINE admission control guarantees only bounded tardiness and not the hard respect of all deadlines. In this case try to select the idle CPU with the largest CPU capacity to minimize tardiness. Favor task_cpu(p) if it has max capacity of !fitting CPUs so that find_later_rq() can potentially still return it (most likely cache-hot) early. Signed-off-by: Luca Abeni <luca.abeni@santannapisa.it> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Juri Lelli <juri.lelli@redhat.com> Link: https://lkml.kernel.org/r/20200520134243.19352-6-dietmar.eggemann@arm.com
-rw-r--r--kernel/sched/cpudeadline.c20
1 files changed, 16 insertions, 4 deletions
diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
index 8630f2a40a3f..8cb06c8c7eb1 100644
--- a/kernel/sched/cpudeadline.c
+++ b/kernel/sched/cpudeadline.c
@@ -121,19 +121,31 @@ int cpudl_find(struct cpudl *cp, struct task_struct *p,
if (later_mask &&
cpumask_and(later_mask, cp->free_cpus, p->cpus_ptr)) {
- int cpu;
+ unsigned long cap, max_cap = 0;
+ int cpu, max_cpu = -1;
if (!static_branch_unlikely(&sched_asym_cpucapacity))
return 1;
/* Ensure the capacity of the CPUs fits the task. */
for_each_cpu(cpu, later_mask) {
- if (!dl_task_fits_capacity(p, cpu))
+ if (!dl_task_fits_capacity(p, cpu)) {
cpumask_clear_cpu(cpu, later_mask);
+
+ cap = capacity_orig_of(cpu);
+
+ if (cap > max_cap ||
+ (cpu == task_cpu(p) && cap == max_cap)) {
+ max_cap = cap;
+ max_cpu = cpu;
+ }
+ }
}
- if (!cpumask_empty(later_mask))
- return 1;
+ if (cpumask_empty(later_mask))
+ cpumask_set_cpu(max_cpu, later_mask);
+
+ return 1;
} else {
int best_cpu = cpudl_maximum(cp);