Here is the best fix for the bug pointed out. Thanks.
I'll try and find pc time to wrap these two patches together and make a v0.32
available.
---
Ensure niced tasks are not inappropriately limiting sleeping unniced tasks
by explicitly checking what the best static priority that has run this
major rotation was.
Reimplement SCHED_BATCH using this check.
Signed-off-by: Con Kolivas <[EMAIL PROTECTED]>
---
kernel/sched.c | 33 ++++++++++++++++++++++++---------
1 file changed, 24 insertions(+), 9 deletions(-)
Index: linux-2.6.21-rc4-mm1/kernel/sched.c
===================================================================
--- linux-2.6.21-rc4-mm1.orig/kernel/sched.c 2007-03-22 12:44:05.000000000
+1100
+++ linux-2.6.21-rc4-mm1/kernel/sched.c 2007-03-22 12:58:26.000000000 +1100
@@ -201,8 +201,11 @@ struct rq {
struct prio_array *active, *expired, arrays[2];
unsigned long *dyn_bitmap, *exp_bitmap;
- int prio_level;
- /* The current dynamic priority level this runqueue is at */
+ int prio_level, best_static_prio;
+ /*
+ * The current dynamic priority level this runqueue is at, and the
+ * best static priority queued this major rotation.
+ */
unsigned long prio_rotation;
/* How many times we have rotated the priority queue */
@@ -704,16 +707,24 @@ static inline int entitled_slot(int stat
/*
* Find the first unused slot by this task that is also in its prio_matrix
- * level.
+ * level. Ensure that the prio_level is not unnecessarily low by checking
+ * that best_static_prio this major rotation was not a niced task.
+ * SCHED_BATCH tasks do not perform this check so they do not induce
+ * latencies in tasks of any nice level.
*/
static inline int next_entitled_slot(struct task_struct *p, struct rq *rq)
{
- DECLARE_BITMAP(tmp, PRIO_RANGE);
+ if (p->static_prio < rq->best_static_prio && p->policy != SCHED_BATCH)
+ return SCHED_PRIO(find_first_zero_bit(p->bitmap, PRIO_RANGE));
+ else {
+ DECLARE_BITMAP(tmp, PRIO_RANGE);
- bitmap_or(tmp, p->bitmap, prio_matrix[USER_PRIO(p->static_prio)],
- PRIO_RANGE);
- return SCHED_PRIO(find_next_zero_bit(tmp, PRIO_RANGE,
- USER_PRIO(rq->prio_level)));
+ bitmap_or(tmp, p->bitmap,
+ prio_matrix[USER_PRIO(p->static_prio)],
+ PRIO_RANGE);
+ return SCHED_PRIO(find_next_zero_bit(tmp, PRIO_RANGE,
+ USER_PRIO(rq->prio_level)));
+ }
}
static void queue_expired(struct task_struct *p, struct rq *rq)
@@ -3315,6 +3326,7 @@ static inline void major_prio_rotation(s
rq->active = new_array;
rq->exp_bitmap = rq->expired->prio_bitmap;
rq->dyn_bitmap = rq->active->prio_bitmap;
+ rq->best_static_prio = MAX_PRIO;
rq->prio_rotation++;
}
@@ -3640,10 +3652,12 @@ need_resched_nonpreemptible:
}
switch_tasks:
if (next == rq->idle) {
+ rq->best_static_prio = MAX_PRIO;
rq->prio_level = MAX_RT_PRIO;
rq->prio_rotation++;
schedstat_inc(rq, sched_goidle);
- }
+ } else if (next->static_prio < rq->best_static_prio)
+ rq->best_static_prio = next->static_prio;
prefetch(next);
prefetch_stack(next);
clear_tsk_need_resched(prev);
@@ -7093,6 +7107,7 @@ void __init sched_init(void)
lockdep_set_class(&rq->lock, &rq->rq_lock_key);
rq->nr_running = 0;
rq->prio_rotation = 0;
+ rq->best_static_prio = MAX_PRIO;
rq->prio_level = MAX_RT_PRIO;
rq->active = rq->arrays;
rq->expired = rq->arrays + 1;
--
-ck
-
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