* [PATCH v6 0/2] Make find_later_rq() choose a closer cpu in topology
@ 2017-08-07 3:50 Byungchul Park
2017-08-07 3:50 ` [PATCH v6 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq() Byungchul Park
` (2 more replies)
0 siblings, 3 replies; 14+ messages in thread
From: Byungchul Park @ 2017-08-07 3:50 UTC (permalink / raw)
To: peterz, mingo; +Cc: linux-kernel, juri.lelli, rostedt, kernel-team
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.
Change from v5
-. exclude two patches already picked up by peterz
(sched/deadline: Make find_later_rq() choose a closer cpu in topology)
(sched/deadline: Change return value of cpudl_find())
-. apply what peterz fixed for 'prefer sibling', into deadline and rt
Change from v4
-. remove a patch that might cause huge lock contention
(by spin lock(&cpudl.lock) in a hot path of scheduler)
Change from v3
-. rename closest_cpu to best_cpu so that it align with rt
-. protect referring cpudl.elements with cpudl.lock
-. change return value of cpudl_find() to bool
Change from v2
-. add support for SD_PREFER_SIBLING
Change from v1
-. clean up the patch
Byungchul Park (2):
sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq()
sched/rt: Add support for SD_PREFER_SIBLING on find_lowest_rq()
kernel/sched/deadline.c | 46 +++++++++++++++++++++++++++++++++++++++++++---
kernel/sched/rt.c | 47 ++++++++++++++++++++++++++++++++++++++++++++---
2 files changed, 87 insertions(+), 6 deletions(-)
--
1.9.1
^ permalink raw reply [flat|nested] 14+ messages in thread
* [PATCH v6 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq()
2017-08-07 3:50 [PATCH v6 0/2] Make find_later_rq() choose a closer cpu in topology Byungchul Park
@ 2017-08-07 3:50 ` Byungchul Park
2017-08-15 15:19 ` Steven Rostedt
2017-08-07 3:50 ` [PATCH v6 2/2] sched/rt: Add support for SD_PREFER_SIBLING on find_lowest_rq() Byungchul Park
2017-08-18 1:25 ` [PATCH v6 0/2] Make find_later_rq() choose a closer cpu in topology Byungchul Park
2 siblings, 1 reply; 14+ messages in thread
From: Byungchul Park @ 2017-08-07 3:50 UTC (permalink / raw)
To: peterz, mingo; +Cc: linux-kernel, juri.lelli, rostedt, kernel-team
It would be better to avoid pushing tasks to other cpu within
a SD_PREFER_SIBLING domain, instead, get more chances to check other
siblings.
Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
kernel/sched/deadline.c | 46 +++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 43 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 0223694..2fd1591 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1319,12 +1319,35 @@ static struct task_struct *pick_earliest_pushable_dl_task(struct rq *rq, int cpu
static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask_dl);
+/*
+ * Find the first cpu in: mask & sd & ~prefer
+ */
+static int find_cpu(const struct cpumask *mask,
+ const struct sched_domain *sd,
+ const struct sched_domain *prefer)
+{
+ const struct cpumask *sds = sched_domain_span(sd);
+ const struct cpumask *ps = prefer ? sched_domain_span(prefer) : NULL;
+ int cpu = -1;
+
+ while ((cpu = cpumask_next(cpu, mask)) < nr_cpu_ids) {
+ if (!cpumask_test_cpu(cpu, sds))
+ continue;
+ if (ps && cpumask_test_cpu(cpu, ps))
+ continue;
+ break;
+ }
+
+ return cpu;
+}
+
static int find_later_rq(struct task_struct *task)
{
- struct sched_domain *sd;
+ struct sched_domain *sd, *prefer = NULL;
struct cpumask *later_mask = this_cpu_cpumask_var_ptr(local_cpu_mask_dl);
int this_cpu = smp_processor_id();
int cpu = task_cpu(task);
+ int fallback_cpu = -1;
/* Make sure the mask is initialized first */
if (unlikely(!later_mask))
@@ -1376,8 +1399,7 @@ static int find_later_rq(struct task_struct *task)
return this_cpu;
}
- best_cpu = cpumask_first_and(later_mask,
- sched_domain_span(sd));
+ best_cpu = find_cpu(later_mask, sd, prefer);
/*
* Last chance: if a cpu being in both later_mask
* and current sd span is valid, that becomes our
@@ -1385,6 +1407,17 @@ static int find_later_rq(struct task_struct *task)
* already under consideration through later_mask.
*/
if (best_cpu < nr_cpu_ids) {
+ /*
+ * If current domain is SD_PREFER_SIBLING
+ * flaged, we have to get more chances to
+ * check other siblings.
+ */
+ if (sd->flags & SD_PREFER_SIBLING) {
+ prefer = sd;
+ if (fallback_cpu == -1)
+ fallback_cpu = best_cpu;
+ continue;
+ }
rcu_read_unlock();
return best_cpu;
}
@@ -1393,6 +1426,13 @@ static int find_later_rq(struct task_struct *task)
rcu_read_unlock();
/*
+ * If fallback_cpu is valid, all our guesses failed *except* for
+ * SD_PREFER_SIBLING domain. Now, we can return the fallback cpu.
+ */
+ if (fallback_cpu != -1)
+ return fallback_cpu;
+
+ /*
* At this point, all our guesses failed, we just return
* 'something', and let the caller sort the things out.
*/
--
1.9.1
^ permalink raw reply related [flat|nested] 14+ messages in thread
* [PATCH v6 2/2] sched/rt: Add support for SD_PREFER_SIBLING on find_lowest_rq()
2017-08-07 3:50 [PATCH v6 0/2] Make find_later_rq() choose a closer cpu in topology Byungchul Park
2017-08-07 3:50 ` [PATCH v6 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq() Byungchul Park
@ 2017-08-07 3:50 ` Byungchul Park
2017-08-10 12:12 ` Byungchul Park
2017-08-18 1:25 ` [PATCH v6 0/2] Make find_later_rq() choose a closer cpu in topology Byungchul Park
2 siblings, 1 reply; 14+ messages in thread
From: Byungchul Park @ 2017-08-07 3:50 UTC (permalink / raw)
To: peterz, mingo; +Cc: linux-kernel, juri.lelli, rostedt, kernel-team
It would be better to avoid pushing tasks to other cpu within
a SD_PREFER_SIBLING domain, instead, get more chances to check other
siblings.
Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
kernel/sched/rt.c | 47 ++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 44 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 979b734..50639e5 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1618,12 +1618,35 @@ static struct task_struct *pick_highest_pushable_task(struct rq *rq, int cpu)
static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask);
+/*
+ * Find the first cpu in: mask & sd & ~prefer
+ */
+static int find_cpu(const struct cpumask *mask,
+ const struct sched_domain *sd,
+ const struct sched_domain *prefer)
+{
+ const struct cpumask *sds = sched_domain_span(sd);
+ const struct cpumask *ps = prefer ? sched_domain_span(prefer) : NULL;
+ int cpu = -1;
+
+ while ((cpu = cpumask_next(cpu, mask)) < nr_cpu_ids) {
+ if (!cpumask_test_cpu(cpu, sds))
+ continue;
+ if (ps && cpumask_test_cpu(cpu, ps))
+ continue;
+ break;
+ }
+
+ return cpu;
+}
+
static int find_lowest_rq(struct task_struct *task)
{
- struct sched_domain *sd;
+ struct sched_domain *sd, *prefer = NULL;
struct cpumask *lowest_mask = this_cpu_cpumask_var_ptr(local_cpu_mask);
int this_cpu = smp_processor_id();
int cpu = task_cpu(task);
+ int fallback_cpu = -1;
/* Make sure the mask is initialized first */
if (unlikely(!lowest_mask))
@@ -1668,9 +1691,20 @@ static int find_lowest_rq(struct task_struct *task)
return this_cpu;
}
- best_cpu = cpumask_first_and(lowest_mask,
- sched_domain_span(sd));
+ best_cpu = find_cpu(lowest_mask, sd, prefer);
+
if (best_cpu < nr_cpu_ids) {
+ /*
+ * If current domain is SD_PREFER_SIBLING
+ * flaged, we have to get more chances to
+ * check other siblings.
+ */
+ if (sd->flags & SD_PREFER_SIBLING) {
+ prefer = sd;
+ if (fallback_cpu == -1)
+ fallback_cpu = best_cpu;
+ continue;
+ }
rcu_read_unlock();
return best_cpu;
}
@@ -1679,6 +1713,13 @@ static int find_lowest_rq(struct task_struct *task)
rcu_read_unlock();
/*
+ * If fallback_cpu is valid, all our quesses failed *except* for
+ * SD_PREFER_SIBLING domain. Now, we can return the fallback cpu.
+ */
+ if (fallback_cpu != -1)
+ return fallback_cpu;
+
+ /*
* And finally, if there were no matches within the domains
* just give the caller *something* to work with from the compatible
* locations.
--
1.9.1
^ permalink raw reply related [flat|nested] 14+ messages in thread
* Re: [PATCH v6 2/2] sched/rt: Add support for SD_PREFER_SIBLING on find_lowest_rq()
2017-08-07 3:50 ` [PATCH v6 2/2] sched/rt: Add support for SD_PREFER_SIBLING on find_lowest_rq() Byungchul Park
@ 2017-08-10 12:12 ` Byungchul Park
0 siblings, 0 replies; 14+ messages in thread
From: Byungchul Park @ 2017-08-10 12:12 UTC (permalink / raw)
To: peterz, mingo; +Cc: linux-kernel, juri.lelli, rostedt, kernel-team
On Mon, Aug 07, 2017 at 12:50:34PM +0900, Byungchul Park wrote:
> It would be better to avoid pushing tasks to other cpu within
> a SD_PREFER_SIBLING domain, instead, get more chances to check other
> siblings.
I applied your suggestion. Could you let me know your opinions about
this?
>
> Signed-off-by: Byungchul Park <byungchul.park@lge.com>
> ---
> kernel/sched/rt.c | 47 ++++++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 44 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 979b734..50639e5 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1618,12 +1618,35 @@ static struct task_struct *pick_highest_pushable_task(struct rq *rq, int cpu)
>
> static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask);
>
> +/*
> + * Find the first cpu in: mask & sd & ~prefer
> + */
> +static int find_cpu(const struct cpumask *mask,
> + const struct sched_domain *sd,
> + const struct sched_domain *prefer)
> +{
> + const struct cpumask *sds = sched_domain_span(sd);
> + const struct cpumask *ps = prefer ? sched_domain_span(prefer) : NULL;
> + int cpu = -1;
> +
> + while ((cpu = cpumask_next(cpu, mask)) < nr_cpu_ids) {
> + if (!cpumask_test_cpu(cpu, sds))
> + continue;
> + if (ps && cpumask_test_cpu(cpu, ps))
> + continue;
> + break;
> + }
> +
> + return cpu;
> +}
> +
> static int find_lowest_rq(struct task_struct *task)
> {
> - struct sched_domain *sd;
> + struct sched_domain *sd, *prefer = NULL;
> struct cpumask *lowest_mask = this_cpu_cpumask_var_ptr(local_cpu_mask);
> int this_cpu = smp_processor_id();
> int cpu = task_cpu(task);
> + int fallback_cpu = -1;
>
> /* Make sure the mask is initialized first */
> if (unlikely(!lowest_mask))
> @@ -1668,9 +1691,20 @@ static int find_lowest_rq(struct task_struct *task)
> return this_cpu;
> }
>
> - best_cpu = cpumask_first_and(lowest_mask,
> - sched_domain_span(sd));
> + best_cpu = find_cpu(lowest_mask, sd, prefer);
> +
> if (best_cpu < nr_cpu_ids) {
> + /*
> + * If current domain is SD_PREFER_SIBLING
> + * flaged, we have to get more chances to
> + * check other siblings.
> + */
> + if (sd->flags & SD_PREFER_SIBLING) {
> + prefer = sd;
> + if (fallback_cpu == -1)
> + fallback_cpu = best_cpu;
> + continue;
> + }
> rcu_read_unlock();
> return best_cpu;
> }
> @@ -1679,6 +1713,13 @@ static int find_lowest_rq(struct task_struct *task)
> rcu_read_unlock();
>
> /*
> + * If fallback_cpu is valid, all our quesses failed *except* for
> + * SD_PREFER_SIBLING domain. Now, we can return the fallback cpu.
> + */
> + if (fallback_cpu != -1)
> + return fallback_cpu;
> +
> + /*
> * And finally, if there were no matches within the domains
> * just give the caller *something* to work with from the compatible
> * locations.
> --
> 1.9.1
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH v6 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq()
2017-08-07 3:50 ` [PATCH v6 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq() Byungchul Park
@ 2017-08-15 15:19 ` Steven Rostedt
2017-08-16 0:38 ` Byungchul Park
0 siblings, 1 reply; 14+ messages in thread
From: Steven Rostedt @ 2017-08-15 15:19 UTC (permalink / raw)
To: Byungchul Park; +Cc: peterz, mingo, linux-kernel, juri.lelli, kernel-team
On Mon, 7 Aug 2017 12:50:33 +0900
Byungchul Park <byungchul.park@lge.com> wrote:
> It would be better to avoid pushing tasks to other cpu within
> a SD_PREFER_SIBLING domain, instead, get more chances to check other
> siblings.
>
> Signed-off-by: Byungchul Park <byungchul.park@lge.com>
> ---
> kernel/sched/deadline.c | 46 +++++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 43 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 0223694..2fd1591 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1319,12 +1319,35 @@ static struct task_struct *pick_earliest_pushable_dl_task(struct rq *rq, int cpu
>
> static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask_dl);
>
> +/*
> + * Find the first cpu in: mask & sd & ~prefer
> + */
> +static int find_cpu(const struct cpumask *mask,
> + const struct sched_domain *sd,
> + const struct sched_domain *prefer)
> +{
> + const struct cpumask *sds = sched_domain_span(sd);
> + const struct cpumask *ps = prefer ? sched_domain_span(prefer) : NULL;
> + int cpu = -1;
> +
> + while ((cpu = cpumask_next(cpu, mask)) < nr_cpu_ids) {
> + if (!cpumask_test_cpu(cpu, sds))
> + continue;
> + if (ps && cpumask_test_cpu(cpu, ps))
> + continue;
> + break;
> + }
> +
> + return cpu;
> +}
> +
> static int find_later_rq(struct task_struct *task)
> {
> - struct sched_domain *sd;
> + struct sched_domain *sd, *prefer = NULL;
> struct cpumask *later_mask = this_cpu_cpumask_var_ptr(local_cpu_mask_dl);
> int this_cpu = smp_processor_id();
> int cpu = task_cpu(task);
> + int fallback_cpu = -1;
>
> /* Make sure the mask is initialized first */
> if (unlikely(!later_mask))
> @@ -1376,8 +1399,7 @@ static int find_later_rq(struct task_struct *task)
> return this_cpu;
> }
>
> - best_cpu = cpumask_first_and(later_mask,
> - sched_domain_span(sd));
> + best_cpu = find_cpu(later_mask, sd, prefer);
> /*
> * Last chance: if a cpu being in both later_mask
> * and current sd span is valid, that becomes our
> @@ -1385,6 +1407,17 @@ static int find_later_rq(struct task_struct *task)
> * already under consideration through later_mask.
> */
> if (best_cpu < nr_cpu_ids) {
> + /*
> + * If current domain is SD_PREFER_SIBLING
> + * flaged, we have to get more chances to
> + * check other siblings.
> + */
> + if (sd->flags & SD_PREFER_SIBLING) {
> + prefer = sd;
Is this how the SD_PREFER_SIBLING works? According to this, the
preferred sd is the next sd in for_each_domain(). Not to mention, the
prefer variable stays set if the next domain has no available CPUs. Is
that what we want?
-- Steve
> + if (fallback_cpu == -1)
> + fallback_cpu = best_cpu;
> + continue;
> + }
> rcu_read_unlock();
> return best_cpu;
> }
> @@ -1393,6 +1426,13 @@ static int find_later_rq(struct task_struct *task)
> rcu_read_unlock();
>
> /*
> + * If fallback_cpu is valid, all our guesses failed *except* for
> + * SD_PREFER_SIBLING domain. Now, we can return the fallback cpu.
> + */
> + if (fallback_cpu != -1)
> + return fallback_cpu;
> +
> + /*
> * At this point, all our guesses failed, we just return
> * 'something', and let the caller sort the things out.
> */
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH v6 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq()
2017-08-15 15:19 ` Steven Rostedt
@ 2017-08-16 0:38 ` Byungchul Park
2017-08-16 1:42 ` Steven Rostedt
0 siblings, 1 reply; 14+ messages in thread
From: Byungchul Park @ 2017-08-16 0:38 UTC (permalink / raw)
To: Steven Rostedt; +Cc: peterz, mingo, linux-kernel, juri.lelli, kernel-team
On Tue, Aug 15, 2017 at 11:19:40AM -0400, Steven Rostedt wrote:
> > @@ -1385,6 +1407,17 @@ static int find_later_rq(struct task_struct *task)
> > * already under consideration through later_mask.
> > */
> > if (best_cpu < nr_cpu_ids) {
> > + /*
> > + * If current domain is SD_PREFER_SIBLING
> > + * flaged, we have to get more chances to
> > + * check other siblings.
> > + */
> > + if (sd->flags & SD_PREFER_SIBLING) {
> > + prefer = sd;
>
> Is this how the SD_PREFER_SIBLING works? According to this, the
> preferred sd is the next sd in for_each_domain(). Not to mention, the
> prefer variable stays set if the next domain has no available CPUs. Is
> that what we want?
Maybe I don't understand what you want to say. The variable, prefer, is
used to pick up the smallest sched domain among SD_PREFER_SIBLING
domains, if more than one SD_PREFER_SIBLING domain exist in the visit.
The prefer variable alway points to the previous SD_PREFER_SIBLING domain.
And that must stay set to be used as a fallback choise if the next domain
has no available CPUs.
Could you explain what I mis-understand?
Thanks,
Byungchul
> -- Steve
>
>
> > + if (fallback_cpu == -1)
> > + fallback_cpu = best_cpu;
> > + continue;
> > + }
> > rcu_read_unlock();
> > return best_cpu;
> > }
> > @@ -1393,6 +1426,13 @@ static int find_later_rq(struct task_struct *task)
> > rcu_read_unlock();
> >
> > /*
> > + * If fallback_cpu is valid, all our guesses failed *except* for
> > + * SD_PREFER_SIBLING domain. Now, we can return the fallback cpu.
> > + */
> > + if (fallback_cpu != -1)
> > + return fallback_cpu;
> > +
> > + /*
> > * At this point, all our guesses failed, we just return
> > * 'something', and let the caller sort the things out.
> > */
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH v6 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq()
2017-08-16 0:38 ` Byungchul Park
@ 2017-08-16 1:42 ` Steven Rostedt
2017-08-16 2:17 ` Byungchul Park
0 siblings, 1 reply; 14+ messages in thread
From: Steven Rostedt @ 2017-08-16 1:42 UTC (permalink / raw)
To: Byungchul Park; +Cc: peterz, mingo, linux-kernel, juri.lelli, kernel-team
On Wed, 16 Aug 2017 09:38:11 +0900
Byungchul Park <byungchul.park@lge.com> wrote:
> On Tue, Aug 15, 2017 at 11:19:40AM -0400, Steven Rostedt wrote:
> > > @@ -1385,6 +1407,17 @@ static int find_later_rq(struct task_struct *task)
> > > * already under consideration through later_mask.
> > > */
> > > if (best_cpu < nr_cpu_ids) {
> > > + /*
> > > + * If current domain is SD_PREFER_SIBLING
> > > + * flaged, we have to get more chances to
> > > + * check other siblings.
BTW, "we have to get more chances" doesn't really make sense. Do you
mean "we need to try other domains"?
> > > + */
> > > + if (sd->flags & SD_PREFER_SIBLING) {
> > > + prefer = sd;
> >
> > Is this how the SD_PREFER_SIBLING works? According to this, the
> > preferred sd is the next sd in for_each_domain(). Not to mention, the
> > prefer variable stays set if the next domain has no available CPUs. Is
> > that what we want?
>
> Maybe I don't understand what you want to say. The variable, prefer, is
> used to pick up the smallest sched domain among SD_PREFER_SIBLING
> domains, if more than one SD_PREFER_SIBLING domain exist in the visit.
>
> The prefer variable alway points to the previous SD_PREFER_SIBLING domain.
> And that must stay set to be used as a fallback choise if the next domain
> has no available CPUs.
>
> Could you explain what I mis-understand?
>
I may be the one confused here ;-)
I think I misread the patch. So, the SD_PREFER_SIBLING means to try to
find a CPU in another sd instead? Thus, we try to find a CPU in a sd
that does not have SD_PREFER_SIBLING set. And if there is none, we use
the preferred sd as a fallback. Is that correct?
I'm not familiar with the SD_PREFER_SIBLING flag, the only
documentation I can find about it is the comment that states:
/* Prefer to place tasks in a sibling domain */
And the very informative git commit change log:
commit b5d978e0c7e79a7ff842e895c85a86b38c71f1cd
Date: Tue Sep 1 10:34:33 2009 +0200
sched: Add SD_PREFER_SIBLING
Do the placement thing using SD flags.
;-)
-- Steve
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH v6 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq()
2017-08-16 1:42 ` Steven Rostedt
@ 2017-08-16 2:17 ` Byungchul Park
2017-08-16 13:32 ` Steven Rostedt
0 siblings, 1 reply; 14+ messages in thread
From: Byungchul Park @ 2017-08-16 2:17 UTC (permalink / raw)
To: Steven Rostedt; +Cc: peterz, mingo, linux-kernel, juri.lelli, kernel-team
On Tue, Aug 15, 2017 at 09:42:01PM -0400, Steven Rostedt wrote:
> > > > @@ -1385,6 +1407,17 @@ static int find_later_rq(struct task_struct *task)
> > > > * already under consideration through later_mask.
> > > > */
> > > > if (best_cpu < nr_cpu_ids) {
> > > > + /*
> > > > + * If current domain is SD_PREFER_SIBLING
> > > > + * flaged, we have to get more chances to
> > > > + * check other siblings.
>
> BTW, "we have to get more chances" doesn't really make sense. Do you
> mean "we need to try other domains"?
Yes, we need to try other domains first if current domain is
SD_PREFER_SIBLING flaged.
> > > > + */
> > > > + if (sd->flags & SD_PREFER_SIBLING) {
> > > > + prefer = sd;
> > >
> > > Is this how the SD_PREFER_SIBLING works? According to this, the
> > > preferred sd is the next sd in for_each_domain(). Not to mention, the
> > > prefer variable stays set if the next domain has no available CPUs. Is
> > > that what we want?
> >
> > Maybe I don't understand what you want to say. The variable, prefer, is
> > used to pick up the smallest sched domain among SD_PREFER_SIBLING
> > domains, if more than one SD_PREFER_SIBLING domain exist in the visit.
> >
> > The prefer variable alway points to the previous SD_PREFER_SIBLING domain.
> > And that must stay set to be used as a fallback choise if the next domain
> > has no available CPUs.
> >
> > Could you explain what I mis-understand?
> >
>
> I may be the one confused here ;-)
>
> I think I misread the patch. So, the SD_PREFER_SIBLING means to try to
> find a CPU in another sd instead? Thus, we try to find a CPU in a sd
> that does not have SD_PREFER_SIBLING set. And if there is none, we use
> the preferred sd as a fallback. Is that correct?
Yes, that's what I intended. IOW:
If (we found a proper sd, not having SD_PREFER_SIBLING?)
use the sd;
else if (we found a proper sd, having SD_PREFER_SIBLING?)
use the smallest sd among SD_PREFER_SIBLING sds;
Thanks,
Byungchul
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH v6 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq()
2017-08-16 2:17 ` Byungchul Park
@ 2017-08-16 13:32 ` Steven Rostedt
2017-08-16 14:04 ` Byungchul Park
0 siblings, 1 reply; 14+ messages in thread
From: Steven Rostedt @ 2017-08-16 13:32 UTC (permalink / raw)
To: Byungchul Park; +Cc: peterz, mingo, linux-kernel, juri.lelli, kernel-team
On Wed, 16 Aug 2017 11:17:36 +0900
Byungchul Park <byungchul.park@lge.com> wrote:
> Yes, that's what I intended. IOW:
>
> If (we found a proper sd, not having SD_PREFER_SIBLING?)
> use the sd;
> else if (we found a proper sd, having SD_PREFER_SIBLING?)
> use the smallest sd among SD_PREFER_SIBLING sds;
BTW, what do you mean by "smallest sd"?
-- Steve
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH v6 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq()
2017-08-16 13:32 ` Steven Rostedt
@ 2017-08-16 14:04 ` Byungchul Park
2017-08-16 14:25 ` Steven Rostedt
0 siblings, 1 reply; 14+ messages in thread
From: Byungchul Park @ 2017-08-16 14:04 UTC (permalink / raw)
To: Steven Rostedt; +Cc: peterz, mingo, linux-kernel, juri.lelli, kernel-team
On Wed, Aug 16, 2017 at 09:32:44AM -0400, Steven Rostedt wrote:
> On Wed, 16 Aug 2017 11:17:36 +0900
> Byungchul Park <byungchul.park@lge.com> wrote:
>
>
> > Yes, that's what I intended. IOW:
> >
> > If (we found a proper sd, not having SD_PREFER_SIBLING?)
> > use the sd;
> > else if (we found a proper sd, having SD_PREFER_SIBLING?)
> > use the smallest sd among SD_PREFER_SIBLING sds;
>
> BTW, what do you mean by "smallest sd"?
There might be more than one SD_PREFER_SIBLING domain in its hierachy.
In that case, we have to choose one of them. Imagine the following
example, in case that the source cpu is cpu 0:
[Domain hierachy for cpu 0]
cpu 0 -+ domain 1 -+
| SD_PREFER_SIBLING flaged |
cpu 1 -+ +- domain 2
| SD_PREFER_SIBLING flaged
cpu 2 -+---------------------------+
|
cpu 3 -+
In this case, we have to choose domain 1 than 2, because cpus in domain 1
are closer to the source cpu, cpu 0. That's what I meant.
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH v6 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq()
2017-08-16 14:04 ` Byungchul Park
@ 2017-08-16 14:25 ` Steven Rostedt
0 siblings, 0 replies; 14+ messages in thread
From: Steven Rostedt @ 2017-08-16 14:25 UTC (permalink / raw)
To: Byungchul Park; +Cc: peterz, mingo, linux-kernel, juri.lelli, kernel-team
On Wed, 16 Aug 2017 23:04:14 +0900
Byungchul Park <byungchul.park@lge.com> wrote:
> On Wed, Aug 16, 2017 at 09:32:44AM -0400, Steven Rostedt wrote:
> > On Wed, 16 Aug 2017 11:17:36 +0900
> > Byungchul Park <byungchul.park@lge.com> wrote:
> >
> >
> > > Yes, that's what I intended. IOW:
> > >
> > > If (we found a proper sd, not having SD_PREFER_SIBLING?)
> > > use the sd;
> > > else if (we found a proper sd, having SD_PREFER_SIBLING?)
> > > use the smallest sd among SD_PREFER_SIBLING sds;
> >
> > BTW, what do you mean by "smallest sd"?
>
> There might be more than one SD_PREFER_SIBLING domain in its hierachy.
> In that case, we have to choose one of them. Imagine the following
> example, in case that the source cpu is cpu 0:
>
> [Domain hierachy for cpu 0]
>
> cpu 0 -+ domain 1 -+
> | SD_PREFER_SIBLING flaged |
> cpu 1 -+ +- domain 2
> | SD_PREFER_SIBLING flaged
> cpu 2 -+---------------------------+
> |
> cpu 3 -+
>
> In this case, we have to choose domain 1 than 2, because cpus in domain 1
> are closer to the source cpu, cpu 0. That's what I meant.
Then you mean "closest sd", at least that makes more sense in the
context.
-- Steve
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH v6 0/2] Make find_later_rq() choose a closer cpu in topology
2017-08-07 3:50 [PATCH v6 0/2] Make find_later_rq() choose a closer cpu in topology Byungchul Park
2017-08-07 3:50 ` [PATCH v6 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq() Byungchul Park
2017-08-07 3:50 ` [PATCH v6 2/2] sched/rt: Add support for SD_PREFER_SIBLING on find_lowest_rq() Byungchul Park
@ 2017-08-18 1:25 ` Byungchul Park
2017-08-18 4:51 ` Joel Fernandes (Google)
2 siblings, 1 reply; 14+ messages in thread
From: Byungchul Park @ 2017-08-18 1:25 UTC (permalink / raw)
To: peterz, mingo; +Cc: linux-kernel, juri.lelli, rostedt, kernel-team
On Mon, Aug 07, 2017 at 12:50:32PM +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.
Could you let me know your opinions about this?
> Change from v5
> -. exclude two patches already picked up by peterz
> (sched/deadline: Make find_later_rq() choose a closer cpu in topology)
> (sched/deadline: Change return value of cpudl_find())
> -. apply what peterz fixed for 'prefer sibling', into deadline and rt
>
> Change from v4
> -. remove a patch that might cause huge lock contention
> (by spin lock(&cpudl.lock) in a hot path of scheduler)
>
> Change from v3
> -. rename closest_cpu to best_cpu so that it align with rt
> -. protect referring cpudl.elements with cpudl.lock
> -. change return value of cpudl_find() to bool
>
> Change from v2
> -. add support for SD_PREFER_SIBLING
>
> Change from v1
> -. clean up the patch
>
> Byungchul Park (2):
> sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq()
> sched/rt: Add support for SD_PREFER_SIBLING on find_lowest_rq()
>
> kernel/sched/deadline.c | 46 +++++++++++++++++++++++++++++++++++++++++++---
> kernel/sched/rt.c | 47 ++++++++++++++++++++++++++++++++++++++++++++---
> 2 files changed, 87 insertions(+), 6 deletions(-)
>
> --
> 1.9.1
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH v6 0/2] Make find_later_rq() choose a closer cpu in topology
2017-08-18 1:25 ` [PATCH v6 0/2] Make find_later_rq() choose a closer cpu in topology Byungchul Park
@ 2017-08-18 4:51 ` Joel Fernandes (Google)
2017-08-18 5:34 ` Byungchul Park
0 siblings, 1 reply; 14+ messages in thread
From: Joel Fernandes (Google) @ 2017-08-18 4:51 UTC (permalink / raw)
To: Byungchul Park
Cc: Peter Zijlstra, mingo, Linux Kernel Mailing List, juri.lelli,
rostedt, kernel-team
On Thu, Aug 17, 2017 at 6:25 PM, Byungchul Park <byungchul.park@lge.com> wrote:
> On Mon, Aug 07, 2017 at 12:50:32PM +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.
>
> Could you let me know your opinions about this?
Patch looks good to me, I would also add a comment ontop of
fallback_cpu (I think Steve mentioned similar thing at [1])
/*
* fallback is the closest CPU in the closest SD incase
* all domains are PREFER_SIBLING
*/
if (fallback_cpu == -1)
fallback_cpu = best_cpu;
And clarify this in the commit message.
thanks,
-Joel
[1] https://patchwork.kernel.org/patch/9884383/
>
>> Change from v5
>> -. exclude two patches already picked up by peterz
>> (sched/deadline: Make find_later_rq() choose a closer cpu in topology)
>> (sched/deadline: Change return value of cpudl_find())
>> -. apply what peterz fixed for 'prefer sibling', into deadline and rt
>>
>> Change from v4
>> -. remove a patch that might cause huge lock contention
>> (by spin lock(&cpudl.lock) in a hot path of scheduler)
>>
>> Change from v3
>> -. rename closest_cpu to best_cpu so that it align with rt
>> -. protect referring cpudl.elements with cpudl.lock
>> -. change return value of cpudl_find() to bool
>>
>> Change from v2
>> -. add support for SD_PREFER_SIBLING
>>
>> Change from v1
>> -. clean up the patch
>>
>> Byungchul Park (2):
>> sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq()
>> sched/rt: Add support for SD_PREFER_SIBLING on find_lowest_rq()
>>
>> kernel/sched/deadline.c | 46 +++++++++++++++++++++++++++++++++++++++++++---
>> kernel/sched/rt.c | 47 ++++++++++++++++++++++++++++++++++++++++++++---
>> 2 files changed, 87 insertions(+), 6 deletions(-)
>>
>> --
>> 1.9.1
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: [PATCH v6 0/2] Make find_later_rq() choose a closer cpu in topology
2017-08-18 4:51 ` Joel Fernandes (Google)
@ 2017-08-18 5:34 ` Byungchul Park
0 siblings, 0 replies; 14+ messages in thread
From: Byungchul Park @ 2017-08-18 5:34 UTC (permalink / raw)
To: Joel Fernandes (Google)
Cc: Peter Zijlstra, mingo, Linux Kernel Mailing List, juri.lelli,
rostedt, kernel-team
On Thu, Aug 17, 2017 at 09:51:34PM -0700, Joel Fernandes (Google) wrote:
> On Thu, Aug 17, 2017 at 6:25 PM, Byungchul Park <byungchul.park@lge.com> wrote:
> > On Mon, Aug 07, 2017 at 12:50:32PM +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.
> >
> > Could you let me know your opinions about this?
>
> Patch looks good to me, I would also add a comment ontop of
> fallback_cpu (I think Steve mentioned similar thing at [1])
>
> /*
> * fallback is the closest CPU in the closest SD incase
> * all domains are PREFER_SIBLING
> */
> if (fallback_cpu == -1)
> fallback_cpu = best_cpu;
>
> And clarify this in the commit message.
Right. I will add it.
Thank you very much,
Byungchul
^ permalink raw reply [flat|nested] 14+ messages in thread
end of thread, other threads:[~2017-08-18 5:35 UTC | newest]
Thread overview: 14+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2017-08-07 3:50 [PATCH v6 0/2] Make find_later_rq() choose a closer cpu in topology Byungchul Park
2017-08-07 3:50 ` [PATCH v6 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq() Byungchul Park
2017-08-15 15:19 ` Steven Rostedt
2017-08-16 0:38 ` Byungchul Park
2017-08-16 1:42 ` Steven Rostedt
2017-08-16 2:17 ` Byungchul Park
2017-08-16 13:32 ` Steven Rostedt
2017-08-16 14:04 ` Byungchul Park
2017-08-16 14:25 ` Steven Rostedt
2017-08-07 3:50 ` [PATCH v6 2/2] sched/rt: Add support for SD_PREFER_SIBLING on find_lowest_rq() Byungchul Park
2017-08-10 12:12 ` Byungchul Park
2017-08-18 1:25 ` [PATCH v6 0/2] Make find_later_rq() choose a closer cpu in topology Byungchul Park
2017-08-18 4:51 ` Joel Fernandes (Google)
2017-08-18 5:34 ` Byungchul Park
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