[PATCH] sched: Make sure task has correct sched_class after policy change

[PATCH] sched: Make sure task has correct sched_class after policy change

[Peter Williams]

>From the code in rt_mutex_setprio(), it is evident that the intention
is that task's with a RT 'prio' value as a consequence of receiving a PI
boost also have their 'sched_class' field set to '&rt_sched_class'.
However, the code in __setscheduler() could result in this intention
being frustrated.

This patch fixes this problem.

Signed-off-by: Peter Williams <pwil3058@bigpond.net.au>

diff --git a/kernel/sched.c b/kernel/sched.c
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6159,6 +6159,8 @@ __setscheduler(struct rq *rq, struct tas
 	p->normal_prio = normal_prio(p);
 	/* we are holding p->pi_lock already */
 	p->prio = rt_mutex_getprio(p);
+	if (rt_prio(prio))
+		p->sched_class = &rt_sched_class;
 	set_load_weight(p);
 }
 

[PATCH] sched: Make sure task has correct sched_class after policy change

[Peter Williams]

>From the code in rt_mutex_setprio(), it is evident that the intention
is that task's with a RT 'prio' value as a consequence of receiving a PI
boost also have their 'sched_class' field set to '&rt_sched_class'.
However, the code in __setscheduler() could result in this intention
being frustrated.

This patch fixes this problem.

Signed-off-by: Peter Williams <pwil3058@bigpond.net.au>

diff --git a/kernel/sched.c b/kernel/sched.c
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6159,6 +6159,8 @@ __setscheduler(struct rq *rq, struct tas
 	p->normal_prio = normal_prio(p);
 	/* we are holding p->pi_lock already */
 	p->prio = rt_mutex_getprio(p);
+	if (rt_prio(p->prio))
+		p->sched_class = &rt_sched_class;
 	set_load_weight(p);
 }
 

Re: [PATCH] sched: Make sure task has correct sched_class after policy change

[Peter Zijlstra]

On Wed, 2009-09-23 at 02:21 +0000, Peter Williams wrote:
> From the code in rt_mutex_setprio(), it is evident that the intention
> is that task's with a RT 'prio' value as a consequence of receiving a PI
> boost also have their 'sched_class' field set to '&rt_sched_class'.
> However, the code in __setscheduler() could result in this intention
> being frustrated.
> 
> This patch fixes this problem.
> 
> Signed-off-by: Peter Williams <pwil3058@bigpond.net.au>

I think you're right, but the problem seems to be that it sets
sched_class based on policy, which seems fragile in the face of PI.

How about the alternative below?

---
 kernel/sched.c |   17 ++++-------------
 1 files changed, 4 insertions(+), 13 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 91843ba..753a52c 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6129,23 +6129,14 @@ __setscheduler(struct rq *rq, struct task_struct *p, int policy, int prio)
 {
 	BUG_ON(p->se.on_rq);
 
-	p->policy = policy;
-	switch (p->policy) {
-	case SCHED_NORMAL:
-	case SCHED_BATCH:
-	case SCHED_IDLE:
-		p->sched_class = &fair_sched_class;
-		break;
-	case SCHED_FIFO:
-	case SCHED_RR:
-		p->sched_class = &rt_sched_class;
-		break;
-	}
-
 	p->rt_priority = prio;
 	p->normal_prio = normal_prio(p);
 	/* we are holding p->pi_lock already */
 	p->prio = rt_mutex_getprio(p);
+	if (rt_prio(p->prio))
+		p->sched_class = &rt_sched_class;
+	else
+		p->sched_class = &fair_sched_class;
 	set_load_weight(p);
 }
 

Re: [PATCH] sched: Make sure task has correct sched_class after policy change

[Peter Williams]

On 23/09/09 16:32, Peter Zijlstra wrote:
> On Wed, 2009-09-23 at 02:21 +0000, Peter Williams wrote:
>>  From the code in rt_mutex_setprio(), it is evident that the intention
>> is that task's with a RT 'prio' value as a consequence of receiving a PI
>> boost also have their 'sched_class' field set to '&rt_sched_class'.
>> However, the code in __setscheduler() could result in this intention
>> being frustrated.
>>
>> This patch fixes this problem.
>>
>> Signed-off-by: Peter Williams<pwil3058@bigpond.net.au>
>
> I think you're right, but the problem seems to be that it sets
> sched_class based on policy, which seems fragile in the face of PI.
>
> How about the alternative below?

Yes, that's what I meant to do i.e. use p->prio in the if condition.  I 
sent a second patch with a fix but your solution is neater :-).

>
> ---
>   kernel/sched.c |   17 ++++-------------
>   1 files changed, 4 insertions(+), 13 deletions(-)
>
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 91843ba..753a52c 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -6129,23 +6129,14 @@ __setscheduler(struct rq *rq, struct task_struct *p, int policy, int prio)
>   {
>   	BUG_ON(p->se.on_rq);
>
> -	p->policy = policy;
> -	switch (p->policy) {
> -	case SCHED_NORMAL:
> -	case SCHED_BATCH:
> -	case SCHED_IDLE:
> -		p->sched_class =&fair_sched_class;
> -		break;
> -	case SCHED_FIFO:
> -	case SCHED_RR:
> -		p->sched_class =&rt_sched_class;
> -		break;
> -	}
> -
>   	p->rt_priority = prio;
>   	p->normal_prio = normal_prio(p);
>   	/* we are holding p->pi_lock already */
>   	p->prio = rt_mutex_getprio(p);
> +	if (rt_prio(p->prio))
> +		p->sched_class =&rt_sched_class;
> +	else
> +		p->sched_class =&fair_sched_class;
>   	set_load_weight(p);
>   }

Peter
-- 
Peter Williams                                   pwil3058@bigpond.net.au

"Learning, n. The kind of ignorance distinguishing the studious."
  -- Ambrose Bierce

Re: [PATCH] sched: Make sure task has correct sched_class after policy change

[Peter Williams]

On 23/09/09 22:40, Peter Williams wrote:
> On 23/09/09 16:32, Peter Zijlstra wrote:
>> On Wed, 2009-09-23 at 02:21 +0000, Peter Williams wrote:
>>> From the code in rt_mutex_setprio(), it is evident that the intention
>>> is that task's with a RT 'prio' value as a consequence of receiving a PI
>>> boost also have their 'sched_class' field set to '&rt_sched_class'.
>>> However, the code in __setscheduler() could result in this intention
>>> being frustrated.
>>>
>>> This patch fixes this problem.
>>>
>>> Signed-off-by: Peter Williams<pwil3058@bigpond.net.au>
>>
>> I think you're right, but the problem seems to be that it sets
>> sched_class based on policy, which seems fragile in the face of PI.
>>
>> How about the alternative below?
>
> Yes, that's what I meant to do i.e. use p->prio in the if condition. I
> sent a second patch with a fix but your solution is neater :-).
>
>>
>> ---
>> kernel/sched.c | 17 ++++-------------
>> 1 files changed, 4 insertions(+), 13 deletions(-)
>>
>> diff --git a/kernel/sched.c b/kernel/sched.c
>> index 91843ba..753a52c 100644
>> --- a/kernel/sched.c
>> +++ b/kernel/sched.c
>> @@ -6129,23 +6129,14 @@ __setscheduler(struct rq *rq, struct
>> task_struct *p, int policy, int prio)
>> {
>> BUG_ON(p->se.on_rq);
>>
>> - p->policy = policy;
>> - switch (p->policy) {
>> - case SCHED_NORMAL:
>> - case SCHED_BATCH:
>> - case SCHED_IDLE:
>> - p->sched_class =&fair_sched_class;
>> - break;
>> - case SCHED_FIFO:
>> - case SCHED_RR:
>> - p->sched_class =&rt_sched_class;
>> - break;
>> - }
>> -
>> p->rt_priority = prio;
>> p->normal_prio = normal_prio(p);
>> /* we are holding p->pi_lock already */
>> p->prio = rt_mutex_getprio(p);
>> + if (rt_prio(p->prio))
>> + p->sched_class =&rt_sched_class;
>> + else
>> + p->sched_class =&fair_sched_class;
>> set_load_weight(p);
>> }
>
> Peter

What ever happened to this patch?  It doesn't seem to have made it into 
the main line yet.

Cheers
Peter
-- 
Peter Williams                                   pwil3058@bigpond.net.au

"Learning, n. The kind of ignorance distinguishing the studious."
  -- Ambrose Bierce

Re: [PATCH] sched: Make sure task has correct sched_class after policy change

[Peter Zijlstra]

On Mon, 2009-10-12 at 10:36 +1000, Peter Williams wrote:

> What ever happened to this patch?  It doesn't seem to have made it into 
> the main line yet.

I,.. uhm,.. guess I'm turning senile and utterly forgot about it.

Queued it, thanks for reminding me!

[tip:sched/urgent] sched: Make sure task has correct sched_class after policy change

[tip-bot for Peter Zijlstra]

Commit-ID:  67d08dfed042855431dc99c9e0e6f6f7e85737ef
Gitweb:     http://git.kernel.org/tip/67d08dfed042855431dc99c9e0e6f6f7e85737ef
Author:     Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Mon, 12 Oct 2009 17:20:54 +0200
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 14 Oct 2009 15:02:35 +0200

sched: Make sure task has correct sched_class after policy change

>From the code in rt_mutex_setprio(), it is evident that the
intention is that task's with a RT 'prio' value as a consequence of
receiving a PI boost also have their 'sched_class' field set to
'&rt_sched_class'.

However, Peter noticed that the code in __setscheduler() could
result in this intention being frustrated. Fix it.

Reported-by: Peter Williams <pwil3058@bigpond.net.au>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1253687579.7695.89.camel@twins>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 kernel/sched.c |   17 ++++-------------
 1 files changed, 4 insertions(+), 13 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 789001d..2d7a002 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6145,23 +6145,14 @@ __setscheduler(struct rq *rq, struct task_struct *p, int policy, int prio)
 {
 	BUG_ON(p->se.on_rq);
 
-	p->policy = policy;
-	switch (p->policy) {
-	case SCHED_NORMAL:
-	case SCHED_BATCH:
-	case SCHED_IDLE:
-		p->sched_class = &fair_sched_class;
-		break;
-	case SCHED_FIFO:
-	case SCHED_RR:
-		p->sched_class = &rt_sched_class;
-		break;
-	}
-
 	p->rt_priority = prio;
 	p->normal_prio = normal_prio(p);
 	/* we are holding p->pi_lock already */
 	p->prio = rt_mutex_getprio(p);
+	if (rt_prio(p->prio))
+		p->sched_class = &rt_sched_class;
+	else
+		p->sched_class = &fair_sched_class;
 	set_load_weight(p);
 }