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Groups > linux.kernel > #1605381 > unrolled thread
| Started by | Byungchul Park <byungchul.park@lge.com> |
|---|---|
| First post | 2017-03-21 09:00 +0100 |
| Last post | 2017-03-23 00:30 +0100 |
| Articles | 5 — 3 participants |
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[PATCH v2] sched/deadline: Make find_later_rq() choose a closer cpu in topology Byungchul Park <byungchul.park@lge.com> - 2017-03-21 09:00 +0100
Re: [PATCH v2] sched/deadline: Make find_later_rq() choose a closer cpu in topology Daniel Bristot de Oliveira <bristot@redhat.com> - 2017-03-21 14:30 +0100
Re: [PATCH v2] sched/deadline: Make find_later_rq() choose a closer cpu in topology Byungchul Park <byungchul.park@lge.com> - 2017-03-22 03:50 +0100
Re: [PATCH v2] sched/deadline: Make find_later_rq() choose a closer cpu in topology Peter Zijlstra <peterz@infradead.org> - 2017-03-22 13:40 +0100
Re: [PATCH v2] sched/deadline: Make find_later_rq() choose a closer cpu in topology Byungchul Park <byungchul.park@lge.com> - 2017-03-23 00:30 +0100
| From | Byungchul Park <byungchul.park@lge.com> |
|---|---|
| Date | 2017-03-21 09:00 +0100 |
| Subject | [PATCH v2] sched/deadline: Make find_later_rq() choose a closer cpu in topology |
| Message-ID | <tnmRX-fw-1@gated-at.bofh.it> |
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 select 0(best_cpu)
even though that's just any among free_cpus. Fix it.
Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
kernel/sched/deadline.c | 29 +++++++++++++++--------------
1 file changed, 15 insertions(+), 14 deletions(-)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index a2ce590..49c93b9 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1324,7 +1324,7 @@ 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))
@@ -1337,17 +1337,14 @@ 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.
@@ -1367,6 +1364,7 @@ static int find_later_rq(struct task_struct *task)
rcu_read_lock();
for_each_domain(cpu, sd) {
if (sd->flags & SD_WAKE_AFFINE) {
+ int closest_cpu;
/*
* If possible, preempting this_cpu is
@@ -1378,14 +1376,17 @@ static int find_later_rq(struct task_struct *task)
return this_cpu;
}
+ closest_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 (closest_cpu < nr_cpu_ids) {
rcu_read_unlock();
- return best_cpu;
+ return closest_cpu;
}
}
}
--
1.9.1
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| From | Daniel Bristot de Oliveira <bristot@redhat.com> |
|---|---|
| Date | 2017-03-21 14:30 +0100 |
| Subject | Re: [PATCH v2] sched/deadline: Make find_later_rq() choose a closer cpu in topology |
| Message-ID | <tns1j-3SO-9@gated-at.bofh.it> |
| In reply to | #1605381 |
On 03/21/2017 08:52 AM, Byungchul Park wrote: > 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 select 0(best_cpu) > even though that's just any among free_cpus. Fix it. That is a nice patch! But I wonder what would be the behavior with your patch in the following hw: # numactl --hardware available: 2 nodes (0-1) node 0 cpus: 0 2 4 6 8 10 12 14 node 0 size: 16159 MB node 0 free: 15308 MB node 1 cpus: 1 3 5 7 9 11 13 15 node 1 size: 16384 MB node 1 free: 15028 MB node distances: node 0 1 0: 10 21 1: 21 10 -- Daniel
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| From | Byungchul Park <byungchul.park@lge.com> |
|---|---|
| Date | 2017-03-22 03:50 +0100 |
| Subject | Re: [PATCH v2] sched/deadline: Make find_later_rq() choose a closer cpu in topology |
| Message-ID | <tnEvw-3Xg-25@gated-at.bofh.it> |
| In reply to | #1605588 |
On Tue, Mar 21, 2017 at 02:28:50PM +0100, Daniel Bristot de Oliveira wrote:
> On 03/21/2017 08:52 AM, Byungchul Park wrote:
> > 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 select 0(best_cpu)
> > even though that's just any among free_cpus. Fix it.
>
> That is a nice patch! But I wonder what would be the behavior with your
> patch in the following hw:
>
> # numactl --hardware
> available: 2 nodes (0-1)
> node 0 cpus: 0 2 4 6 8 10 12 14
> node 0 size: 16159 MB
> node 0 free: 15308 MB
> node 1 cpus: 1 3 5 7 9 11 13 15
> node 1 size: 16384 MB
> node 1 free: 15028 MB
> node distances:
> node 0 1
> 0: 10 21
> 1: 21 10
Hi,
In this case, I guess the topology looks like:
0 --+
+--+
2 --+ |
+-- ... --+
4 --+ | |
+--+ |
6 --+ |
... ...
9 --+ |
+--+ |
11 --+ | |
+-- ... -+
13 --+ |
+--+
15 --+
And sched_domain would also reflect that. So the dl's push works well.
Do I miss something?
In addition, IMHO, it's not an issue for dl's push but one for building
sched_domains. Wrong?
Thanks,
Byungchul
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| From | Peter Zijlstra <peterz@infradead.org> |
|---|---|
| Date | 2017-03-22 13:40 +0100 |
| Subject | Re: [PATCH v2] sched/deadline: Make find_later_rq() choose a closer cpu in topology |
| Message-ID | <tnNIt-2p2-17@gated-at.bofh.it> |
| In reply to | #1605381 |
On Tue, Mar 21, 2017 at 04:52:24PM +0900, Byungchul Park wrote: > 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 select 0(best_cpu) > even though that's just any among free_cpus. Fix it. This would result in picking the HT sibling, if available. Which is typically the worst possible pick. If you add support for SD_PREFER_SIBLING, which denotes a preference for any other sibling domain above this one, this might work.
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| From | Byungchul Park <byungchul.park@lge.com> |
|---|---|
| Date | 2017-03-23 00:30 +0100 |
| Subject | Re: [PATCH v2] sched/deadline: Make find_later_rq() choose a closer cpu in topology |
| Message-ID | <tnXRv-1Qw-1@gated-at.bofh.it> |
| In reply to | #1606425 |
On Wed, Mar 22, 2017 at 01:37:28PM +0100, Peter Zijlstra wrote: > On Tue, Mar 21, 2017 at 04:52:24PM +0900, Byungchul Park wrote: > > 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 select 0(best_cpu) > > even though that's just any among free_cpus. Fix it. > > This would result in picking the HT sibling, if available. Which is > typically the worst possible pick. > > If you add support for SD_PREFER_SIBLING, which denotes a preference for > any other sibling domain above this one, this might work. Sure. I will add that support as well. Thank you.
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