Problem:
The advent of priority inheritance (PI) (in -mm kernels) means that the
prio field for non real time tasks can no longer be guaranteed to be
greater than or equal to MAX_RT_PRIO. This, in turn, means that the
rt_task() macro is no longer a reliable test for determining if the
scheduler policy of a task is one of the real time policies.
Redefining rt_task() is not a good solution as the majority places
where it is used within sched.c the current definition is what is
required. However, this is not the case in the functions
set_load_weight() and set_user_nice() (and perhaps elsewhere in the
kernel).
Solution:
Define a new macro, has_rt_policy(), that returns true if the task given
as an argument has a policy of SCHED_RR or SCHED_FIFO and use this
inside set_load_weight() and set_user_nice(). The definition is made in
sched.h so that it is generally available should it be needed elsewhere
in the kernel.
Signed-off-by: Peter Williams <[email protected]>
include/linux/sched.h | 2 ++
kernel/sched.c | 15 +++++++--------
2 files changed, 9 insertions(+), 8 deletions(-)
Index: MM-2.6.17-rc4-mm3/include/linux/sched.h
===================================================================
--- MM-2.6.17-rc4-mm3.orig/include/linux/sched.h 2006-05-26 10:39:59.000000000 +1000
+++ MM-2.6.17-rc4-mm3/include/linux/sched.h 2006-05-26 10:43:21.000000000 +1000
@@ -491,6 +491,8 @@ struct signal_struct {
#define rt_prio(prio) unlikely((prio) < MAX_RT_PRIO)
#define rt_task(p) rt_prio((p)->prio)
#define batch_task(p) (unlikely((p)->policy == SCHED_BATCH))
+#define has_rt_policy(p) \
+ unlikely((p)->policy != SCHED_NORMAL && (p)->policy != SCHED_BATCH)
/*
* Some day this will be a full-fledged user tracking system..
Index: MM-2.6.17-rc4-mm3/kernel/sched.c
===================================================================
--- MM-2.6.17-rc4-mm3.orig/kernel/sched.c 2006-05-26 10:39:59.000000000 +1000
+++ MM-2.6.17-rc4-mm3/kernel/sched.c 2006-05-26 10:44:51.000000000 +1000
@@ -786,7 +786,7 @@ static inline int expired_starving(runqu
static void set_load_weight(task_t *p)
{
- if (rt_task(p)) {
+ if (has_rt_policy(p)) {
#ifdef CONFIG_SMP
if (p == task_rq(p)->migration_thread)
/*
@@ -835,7 +835,7 @@ static inline int normal_prio(task_t *p)
{
int prio;
- if (p->policy != SCHED_NORMAL && p->policy != SCHED_BATCH)
+ if (has_rt_policy(p))
prio = MAX_RT_PRIO-1 - p->rt_priority;
else
prio = __normal_prio(p);
@@ -3831,7 +3831,7 @@ void set_user_nice(task_t *p, long nice)
unsigned long flags;
prio_array_t *array;
runqueue_t *rq;
- int old_prio, new_prio, delta;
+ int old_prio, delta;
if (TASK_NICE(p) == nice || nice < -20 || nice > 19)
return;
@@ -3846,7 +3846,7 @@ void set_user_nice(task_t *p, long nice)
* it wont have any effect on scheduling until the task is
* not SCHED_NORMAL/SCHED_BATCH:
*/
- if (rt_task(p)) {
+ if (has_rt_policy(p)) {
p->static_prio = NICE_TO_PRIO(nice);
goto out_unlock;
}
@@ -3856,12 +3856,11 @@ void set_user_nice(task_t *p, long nice)
dec_raw_weighted_load(rq, p);
}
- old_prio = p->prio;
- new_prio = NICE_TO_PRIO(nice);
- delta = new_prio - old_prio;
p->static_prio = NICE_TO_PRIO(nice);
set_load_weight(p);
- p->prio += delta;
+ old_prio = p->prio;
+ p->prio = effective_prio(p);
+ delta = p->prio - old_prio;
if (array) {
enqueue_task(p, array);
--
Peter Williams [email protected]
"Learning, n. The kind of ignorance distinguishing the studious."
-- Ambrose Bierce
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