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SubjectRe: [PATCH] sched: Make sure task has correct sched_class after policy change
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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);
}




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