Re:[PATCH]sched/rt: Do not try to push tasks if pinned task switches to RT

Re:[PATCH]sched/rt: Do not try to push tasks if pinned task switches to RT

[Kirill Tkhai]

> On Tue, 2013-01-29 at 00:23 +0400, Kirill Tkhai wrote:
> 
>> Just switched pinned task is not able to be pushed. If the rq had had
>> several RT tasks before they have already been considered as candidates
>> to be pushed (or pulled).
> 
> Thanks, but I have one minor nit.
> 
>> Signed-off-by: Kirill V Tkhai <tkhai@yandex.ru>
>> CC: Steven Rostedt <rostedt@goodmis.org>
>> CC: Ingo Molnar <mingo@kernel.org>
>> CC: Peter Zijlstra <peterz@infradead.org>
>> CC: linux-rt-users <linux-rt-users@vger.kernel.org>
>> ---
>> kernel/sched/rt.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
>> index 4e8f0f4..5f7d92b 100644
>> --- a/kernel/sched/rt.c
>> +++ b/kernel/sched/rt.c
>> @@ -1925,9 +1925,9 @@ static void switched_to_rt(struct rq *rq, struct task_struct *p)
>> */
>> if (p->on_rq && rq->curr != p) {
>> #ifdef CONFIG_SMP
>> - if (rq->rt.overloaded && push_rt_task(rq) &&
>> + if (rq->rt.overloaded && p->nr_cpus_allowed > 1 &&
> 
> I would swap the order here. That is, check p->nr_cpus_allowed before
> rq->rt.overloaded. The order doesn't really matter, and even though
> rq->rt.overloaded is probably more likely to be 0, it is used by other
> CPUs. And as a micro-optimization, I rather read something that is used
> by only one CPU than to read something that may be modified by many
> CPUs.
> 
> -- Steve
> 

I corrected. Thanks.

[PATCH]sched/rt: Do not try to push tasks if pinned task switches to RT

Just switched pinned task is not able to be pushed. If the rq had had
several RT tasks before they have already been considered as candidates
to be pushed (or pulled).

Signed-off-by: Kirill V Tkhai <tkhai@yandex.ru>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Ingo Molnar <mingo@kernel.org>
CC: Peter Zijlstra <peterz@infradead.org>
CC: linux-rt-users <linux-rt-users@vger.kernel.org>
---
 kernel/sched/rt.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 4e8f0f4..5aab032 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1925,9 +1925,9 @@ static void switched_to_rt(struct rq *rq, struct task_struct *p)
 	 */
 	if (p->on_rq && rq->curr != p) {
 #ifdef CONFIG_SMP
-		if (rq->rt.overloaded && push_rt_task(rq) &&
+		if (p->nr_cpus_allowed > 1 && rq->rt.overloaded &&
 		    /* Don't resched if we changed runqueues */
-		    rq != task_rq(p))
+		    push_rt_task(rq) && rq != task_rq(p))
 			check_resched = 0;
 #endif /* CONFIG_SMP */
 		if (check_resched && p->prio < rq->curr->prio)

Re: [PATCH]sched/rt: Do not try to push tasks if pinned task switches to RT

[Steven Rostedt]

Peter,

I'm going through my inbox (over a year old), and found this patch from
Kirill. It looks fine to me. You can apply it with my

  Acked-by: Steven Rostedt <rostedt@goodmis.org>

-- Steve

[PATCH]sched/rt: Do not try to push tasks if pinned task switches to RT

Just switched pinned task is not able to be pushed. If the rq had had
several RT tasks before they have already been considered as candidates
to be pushed (or pulled).

Signed-off-by: Kirill V Tkhai <tkhai@yandex.ru>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Ingo Molnar <mingo@kernel.org>
CC: Peter Zijlstra <peterz@infradead.org>
CC: linux-rt-users <linux-rt-users@vger.kernel.org>
---
 kernel/sched/rt.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 4e8f0f4..5aab032 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1925,9 +1925,9 @@ static void switched_to_rt(struct rq *rq, struct task_struct *p)
 	 */
 	if (p->on_rq && rq->curr != p) {
 #ifdef CONFIG_SMP
-		if (rq->rt.overloaded && push_rt_task(rq) &&
+		if (p->nr_cpus_allowed > 1 && rq->rt.overloaded &&
 		    /* Don't resched if we changed runqueues */
-		    rq != task_rq(p))
+		    push_rt_task(rq) && rq != task_rq(p))
 			check_resched = 0;
 #endif /* CONFIG_SMP */
 		if (check_resched && p->prio < rq->curr->prio)

Re: [PATCH]sched/rt: Do not try to push tasks if pinned task switches to RT

[Nicholas Mc Guire]

On Wed, 12 Mar 2014, Steven Rostedt wrote:

> Peter,
> 
> I'm going through my inbox (over a year old), and found this patch from
> Kirill. It looks fine to me. You can apply it with my
> 
>   Acked-by: Steven Rostedt <rostedt@goodmis.org>
>
> -- Steve
> 
> [PATCH]sched/rt: Do not try to push tasks if pinned task switches to RT
> 
> Just switched pinned task is not able to be pushed. If the rq had had
> several RT tasks before they have already been considered as candidates
> to be pushed (or pulled).
> 
> Signed-off-by: Kirill V Tkhai <tkhai@yandex.ru>
> CC: Steven Rostedt <rostedt@goodmis.org>
> CC: Ingo Molnar <mingo@kernel.org>
> CC: Peter Zijlstra <peterz@infradead.org>
> CC: linux-rt-users <linux-rt-users@vger.kernel.org>
> ---
>  kernel/sched/rt.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 4e8f0f4..5aab032 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1925,9 +1925,9 @@ static void switched_to_rt(struct rq *rq, struct task_struct *p)
>  	 */
>  	if (p->on_rq && rq->curr != p) {
>  #ifdef CONFIG_SMP
> -		if (rq->rt.overloaded && push_rt_task(rq) &&
> +		if (p->nr_cpus_allowed > 1 && rq->rt.overloaded &&
>  		    /* Don't resched if we changed runqueues */
> -		    rq != task_rq(p))
> +		    push_rt_task(rq) && rq != task_rq(p))
>  			check_resched = 0;
>  #endif /* CONFIG_SMP */
>  		if (check_resched && p->prio < rq->curr->prio)

would there not need to be a check for p->migrate_disable ?
push_rt_task() is not checking and so a high prio RT task 
preemting a low prio RT task in a migrate_disable() section
would actually push it off this cpu ? atleast I did not 
find why that would not happen.

thx!
hofrat

Re: [PATCH]sched/rt: Do not try to push tasks if pinned task switches to RT

[Kirill Tkhai]

12.03.2014, 14:39, "Nicholas Mc Guire" <der.herr@hofr.at>:
> On Wed, 12 Mar 2014, Steven Rostedt wrote:
>
>>  Peter,
>>
>>  I'm going through my inbox (over a year old), and found this patch from
>>  Kirill. It looks fine to me. You can apply it with my
>>
>>    Acked-by: Steven Rostedt <rostedt@goodmis.org>
>>
>>  -- Steve
>>
>>  [PATCH]sched/rt: Do not try to push tasks if pinned task switches to RT
>>
>>  Just switched pinned task is not able to be pushed. If the rq had had
>>  several RT tasks before they have already been considered as candidates
>>  to be pushed (or pulled).
>>
>>  Signed-off-by: Kirill V Tkhai <tkhai@yandex.ru>
>>  CC: Steven Rostedt <rostedt@goodmis.org>
>>  CC: Ingo Molnar <mingo@kernel.org>
>>  CC: Peter Zijlstra <peterz@infradead.org>
>>  CC: linux-rt-users <linux-rt-users@vger.kernel.org>
>>  ---
>>   kernel/sched/rt.c |    4 ++--
>>   1 files changed, 2 insertions(+), 2 deletions(-)
>>  diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
>>  index 4e8f0f4..5aab032 100644
>>  --- a/kernel/sched/rt.c
>>  +++ b/kernel/sched/rt.c
>>  @@ -1925,9 +1925,9 @@ static void switched_to_rt(struct rq *rq, struct task_struct *p)
>>            */
>>           if (p->on_rq && rq->curr != p) {
>>   #ifdef CONFIG_SMP
>>  - if (rq->rt.overloaded && push_rt_task(rq) &&
>>  + if (p->nr_cpus_allowed > 1 && rq->rt.overloaded &&
>>                       /* Don't resched if we changed runqueues */
>>  -    rq != task_rq(p))
>>  +    push_rt_task(rq) && rq != task_rq(p))
>>                           check_resched = 0;
>>   #endif /* CONFIG_SMP */
>>                   if (check_resched && p->prio < rq->curr->prio)
>
> would there not need to be a check for p->migrate_disable ?
> push_rt_task() is not checking and so a high prio RT task
> preemting a low prio RT task in a migrate_disable() section
> would actually push it off this cpu ? atleast I did not
> find why that would not happen.

Hi, Nicholas!

p is not rq->curr, so its p->migrate_disable state is already updated and
it can't be pushed (nr_cpus_allowed == 1 and it's not pushable).

(If I understand right, that you worry about this).

Kirill

> thx!
> hofrat

Re: [PATCH]sched/rt: Do not try to push tasks if pinned task switches to RT

[Steven Rostedt]

On Wed, 12 Mar 2014 16:23:48 +0400
Kirill Tkhai <tkhai@yandex.ru> wrote:

> > would there not need to be a check for p->migrate_disable ?
> > push_rt_task() is not checking and so a high prio RT task
> > preemting a low prio RT task in a migrate_disable() section
> > would actually push it off this cpu ? atleast I did not
> > find why that would not happen.
> 
> Hi, Nicholas!
> 
> p is not rq->curr, so its p->migrate_disable state is already updated and
> it can't be pushed (nr_cpus_allowed == 1 and it's not pushable).
> 
> (If I understand right, that you worry about this).
> 

Correct. If p has migrate_disabled set and scheduled out, then when it
gets scheduled out, its cpu affinity gets set to only the current cpu
and nr_cpu_allowed to 1. No need to check here if p->migrate_disabled is
set.

-- Steve

Re: [PATCH]sched/rt: Do not try to push tasks if pinned task switches to RT

[Peter Zijlstra]

On Wed, Mar 12, 2014 at 06:18:33AM -0400, Steven Rostedt wrote:
> Peter,
> 
> I'm going through my inbox (over a year old), and found this patch from
> Kirill. It looks fine to me. You can apply it with my
> 

Thanks!

[tip:sched/core] sched/rt: Do not try to push tasks if pinned task switches to RT

[tip-bot for Kirill V Tkhai]

Commit-ID:  10447917551e0fffb8d1892d46e633c3e0a9c1ec
Gitweb:     http://git.kernel.org/tip/10447917551e0fffb8d1892d46e633c3e0a9c1ec
Author:     Kirill V Tkhai <tkhai@yandex.ru>
AuthorDate: Wed, 12 Mar 2014 06:18:33 -0400
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 18 Apr 2014 12:07:23 +0200

sched/rt: Do not try to push tasks if pinned task switches to RT

Just switched pinned task is not able to be pushed. If the rq had had
several RT tasks before they have already been considered as candidates
to be pushed (or pulled).

Signed-off-by: Kirill V Tkhai <tkhai@yandex.ru>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20140312061833.3a43aa64@gandalf.local.home
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/rt.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index bd2267a..1e4992e 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1892,9 +1892,9 @@ static void switched_to_rt(struct rq *rq, struct task_struct *p)
 	 */
 	if (p->on_rq && rq->curr != p) {
 #ifdef CONFIG_SMP
-		if (rq->rt.overloaded && push_rt_task(rq) &&
+		if (p->nr_cpus_allowed > 1 && rq->rt.overloaded &&
 		    /* Don't resched if we changed runqueues */
-		    rq != task_rq(p))
+		    push_rt_task(rq) && rq != task_rq(p))
 			check_resched = 0;
 #endif /* CONFIG_SMP */
 		if (check_resched && p->prio < rq->curr->prio)

Re:[PATCH]sched/rt: Do not try to push tasks if pinned task switches to RT

[Kirill Tkhai]

> From: Libo Chen <libo.chen@huawei.com>
> 
> On 2013-1-29 4:23, Kirill Tkhai wrote:
> 
>> Just switched pinned task is not able to be pushed. If the rq had had
>> several RT tasks before they have already been considered as candidates
>> to be pushed (or pulled).
>>
>> Signed-off-by: Kirill V Tkhai <tkhai@yandex.ru>
>> CC: Steven Rostedt <rostedt@goodmis.org>
>> CC: Ingo Molnar <mingo@kernel.org>
>> CC: Peter Zijlstra <peterz@infradead.org>
>> CC: linux-rt-users <linux-rt-users@vger.kernel.org>
>> ---
>> kernel/sched/rt.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
>> index 4e8f0f4..5f7d92b 100644
>> --- a/kernel/sched/rt.c
>> +++ b/kernel/sched/rt.c
>> @@ -1925,9 +1925,9 @@ static void switched_to_rt(struct rq *rq, struct task_struct *p)
>> */
>> if (p->on_rq && rq->curr != p) {
>> #ifdef CONFIG_SMP
>> - if (rq->rt.overloaded && push_rt_task(rq) &&
>> + if (rq->rt.overloaded && p->nr_cpus_allowed > 1 &&
>> /* Don't resched if we changed runqueues */
>> - rq != task_rq(p))
>> + push_rt_task(rq) && rq != task_rq(p))
> 
> I think you worry about it was excess to call push_rt_task, since the task of p->nr_cpus_allowed=1 can`t be pushed. is that right?

Sure.

> 
> The task of p->nr_cpus_allowed =1 would`t be added to pushable_tasks list （see the enqueue_task_rt()）and this push_rt_task() need to push other tasks when rt.overloaded.

If rq has already had 2 or more pushable tasks and we try to add a pinned task then call of push_rt_task will just waste a time.

> 
> So I don`t agree this patch.
> 
>> check_resched = 0;
>> #endif /* CONFIG_SMP */
>> if (check_resched && p->prio < rq->curr->prio)
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in
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 -- 

Re: Re:[PATCH]sched/rt: Do not try to push tasks if pinned task switches to RT

[Steven Rostedt]

On Tue, 2013-01-29 at 13:13 +0400, Kirill Tkhai wrote:

> > 
> > The task of p->nr_cpus_allowed =1 would`t be added to pushable_tasks list （see the enqueue_task_rt()）and this push_rt_task() need to push other tasks when rt.overloaded.
> 
> If rq has already had 2 or more pushable tasks and we try to add a pinned task then call of push_rt_task will just waste a time.
> 

Correct, I just have some minor comments about the patch.

-- Steve