Commit-ID: b18c3ca11c20caa4a397baa9b893ebc4aaa4fe9f
Gitweb: http://git.kernel.org/tip/b18c3ca11c20caa4a397baa9b893ebc4aaa4fe9f
Author: Byungchul Park <byungchul.park@xxxxxxx>
AuthorDate: Tue, 23 May 2017 11:00:56 +0900
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 10 Aug 2017 12:18:17 +0200
sched/deadline: Make find_later_rq() choose a closer CPU in topology
When cpudl_find() returns any among free_cpus, the CPU might not be
closer than others, considering sched domain. For example:
this_cpu: 15
free_cpus: 0, 1,..., 14 (== later_mask)
best_cpu: 0
topology:
0 --+
+--+
1 --+ |
+-- ... --+
2 --+ | |
+--+ |
3 --+ |
... ...
12 --+ |
+--+ |
13 --+ | |
+-- ... -+
14 --+ |
+--+
15 --+
In this case, it would be best to select 14 since it's a free CPU and
closest to 15 (this_cpu). However, currently the code selects 0 (best_cpu)
even though that's just any among free_cpus. Fix it.
This (re)aligns the deadline behaviour with the rt behaviour.
Signed-off-by: Byungchul Park <byungchul.park@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: <bristot@xxxxxxxxxx>
Cc: <juri.lelli@xxxxxxxxx>
Cc: <kernel-team@xxxxxxx>
Cc: <rostedt@xxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1495504859-10960-2-git-send-email-byungchul.park@xxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/sched/deadline.c | 27 ++++++++++++++-------------
1 file changed, 14 insertions(+), 13 deletions(-)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index a205ac7..ac07d7c 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1798,7 +1798,7 @@ static int find_later_rq(struct task_struct *task)
struct sched_domain *sd;
struct cpumask *later_mask = this_cpu_cpumask_var_ptr(local_cpu_mask_dl);
int this_cpu = smp_processor_id();
- int best_cpu, cpu = task_cpu(task);
+ int cpu = task_cpu(task);
/* Make sure the mask is initialized first */
if (unlikely(!later_mask))
@@ -1811,17 +1811,14 @@ static int find_later_rq(struct task_struct *task)
* We have to consider system topology and task affinity
* first, then we can look for a suitable cpu.
*/
- best_cpu = cpudl_find(&task_rq(task)->rd->cpudl,
- task, later_mask);
- if (best_cpu == -1)
+ if (cpudl_find(&task_rq(task)->rd->cpudl, task, later_mask) == -1)
return -1;
/*
- * If we are here, some target has been found,
- * the most suitable of which is cached in best_cpu.
- * This is, among the runqueues where the current tasks
- * have later deadlines than the task's one, the rq
- * with the latest possible one.
+ * If we are here, some targets have been found, including
+ * the most suitable which is, among the runqueues where the
+ * current tasks have later deadlines than the task's one, the
+ * rq with the latest possible one.
*
* Now we check how well this matches with task's
* affinity and system topology.
@@ -1841,6 +1838,7 @@ static int find_later_rq(struct task_struct *task)
rcu_read_lock();
for_each_domain(cpu, sd) {
if (sd->flags & SD_WAKE_AFFINE) {
+ int best_cpu;
/*
* If possible, preempting this_cpu is
@@ -1852,12 +1850,15 @@ static int find_later_rq(struct task_struct *task)
return this_cpu;
}
+ best_cpu = cpumask_first_and(later_mask,
+ sched_domain_span(sd));
/*
- * Last chance: if best_cpu is valid and is
- * in the mask, that becomes our choice.
+ * Last chance: if a cpu being in both later_mask
+ * and current sd span is valid, that becomes our
+ * choice. Of course, the latest possible cpu is
+ * already under consideration through later_mask.
*/
- if (best_cpu < nr_cpu_ids &&
- cpumask_test_cpu(best_cpu, sched_domain_span(sd))) {
+ if (best_cpu < nr_cpu_ids) {
rcu_read_unlock();
return best_cpu;
}
--
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