From: luca abeni <luca.ab...@santannapisa.it>
Currently, the SCHED_DEADLINE scheduler uses a global EDF scheduling
algorithm, migrating tasks to CPU cores without considering the core
capacity and the task utilization. This works well on homogeneous
systems (SCHED_DEADLINE tasks are guaranteed to have a bounded
tardiness), but presents some issues on heterogeneous systems. For
example, a SCHED_DEADLINE task might be migrated on a core that has not
enough processing capacity to correctly serve the task (think about a
task with runtime 70ms and period 100ms migrated to a core with
processing capacity 0.5)
This commit is a first step to address the issue: When a task wakes
up or migrates away from a CPU core, the scheduler tries to find an
idle core having enough processing capacity to serve the task.
Signed-off-by: luca abeni <luca.ab...@santannapisa.it>
---
kernel/sched/cpudeadline.c | 31 +++++++++++++++++++++++++++++--
kernel/sched/deadline.c | 8 ++++++--
kernel/sched/sched.h | 7 ++++++-
3 files changed, 41 insertions(+), 5 deletions(-)
diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
index 50316455ea66..d21f7905b9c1 100644
--- a/kernel/sched/cpudeadline.c
+++ b/kernel/sched/cpudeadline.c
@@ -110,6 +110,22 @@ static inline int cpudl_maximum(struct cpudl *cp)
return cp->elements[0].cpu;
}
+static inline int dl_task_fit(const struct sched_dl_entity *dl_se,
+ int cpu, u64 *c)
+{
+ u64 cap = (arch_scale_cpu_capacity(NULL, cpu) *
arch_scale_freq_capacity(cpu)) >> SCHED_CAPACITY_SHIFT;
+ s64 rel_deadline = dl_se->dl_deadline;
+ u64 rem_runtime = dl_se->dl_runtime;
+
+ if (c)
+ *c = cap;
+
+ if ((rel_deadline * cap) >> SCHED_CAPACITY_SHIFT < rem_runtime)
+ return 0;
+
+ return 1;
+}
+
/*
* cpudl_find - find the best (later-dl) CPU in the system
* @cp: the cpudl max-heap context
@@ -125,8 +141,19 @@ int cpudl_find(struct cpudl *cp, struct task_struct *p,
if (later_mask &&
cpumask_and(later_mask, cp->free_cpus, &p->cpus_allowed)) {
- return 1;
- } else {
+ int cpu;
+
+ for_each_cpu(cpu, later_mask) {
+ u64 cap;
+
+ if (!dl_task_fit(&p->dl, cpu, &cap))
+ cpumask_clear_cpu(cpu, later_mask);
+ }
+
+ if (!cpumask_empty(later_mask))
+ return 1;
+ }
+ {
int best_cpu = cpudl_maximum(cp);
WARN_ON(best_cpu != -1 && !cpu_present(best_cpu));
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 5b981eeeb944..3436f3d8fa8f 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1584,6 +1584,9 @@ select_task_rq_dl(struct task_struct *p, int cpu, int
sd_flag, int flags)
if (sd_flag != SD_BALANCE_WAKE)
goto out;
+ if (dl_entity_is_special(&p->dl))
+ goto out;
+
rq = cpu_rq(cpu);
rcu_read_lock();
@@ -1598,10 +1601,11 @@ select_task_rq_dl(struct task_struct *p, int cpu, int
sd_flag, int flags)
* other hand, if it has a shorter deadline, we
* try to make it stay here, it might be important.
*/
- if (unlikely(dl_task(curr)) &&
+ if ((unlikely(dl_task(curr)) &&
(curr->nr_cpus_allowed < 2 ||
!dl_entity_preempt(&p->dl, &curr->dl)) &&
- (p->nr_cpus_allowed > 1)) {
+ (p->nr_cpus_allowed > 1)) ||
+ static_branch_unlikely(&sched_asym_cpucapacity)) {
int target = find_later_rq(p);
if (target != -1 &&
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 32d242694863..e5f9fd3aee80 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2367,7 +2367,12 @@ unsigned long schedutil_cpu_util(int cpu, unsigned long
util_cfs,
static inline unsigned long cpu_bw_dl(struct rq *rq)
{
- return (rq->dl.running_bw * SCHED_CAPACITY_SCALE) >> BW_SHIFT;
+ unsigned long res;
+
+ res = (rq->dl.running_bw * SCHED_CAPACITY_SCALE) >> BW_SHIFT;
+
+ return (res << SCHED_CAPACITY_SHIFT) /
+ arch_scale_cpu_capacity(NULL, rq->cpu);
}
static inline unsigned long cpu_util_dl(struct rq *rq)
--
2.20.1
