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Subject[PATCH 3/2] sched/cpupri: Remap CPUPRI_NORMAL to MAX_RT_PRIO-1

This makes the mapping continuous and frees up 100 for other usage.

Prev mapping:

p->rt_priority p->prio newpri cpupri

-1 -1 (CPUPRI_INVALID)

100 0 (CPUPRI_NORMAL)

1 98 98 1
...
49 50 50 49
50 49 49 50
...
99 0 0 99

New mapping:

p->rt_priority p->prio newpri cpupri

-1 -1 (CPUPRI_INVALID)

99 0 (CPUPRI_NORMAL)

1 98 98 1
...
49 50 50 49
50 49 49 50
...
99 0 0 99

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
kernel/sched/cpupri.c | 34 +++++++++++++++++++++++++++-------
kernel/sched/rt.c | 16 +++++++++-------
2 files changed, 36 insertions(+), 14 deletions(-)

--- a/kernel/sched/cpupri.c
+++ b/kernel/sched/cpupri.c
@@ -24,17 +24,37 @@
*/
#include "sched.h"

-/* Convert between a 140 based task->prio, and our 100 based cpupri */
+/*
+ * p->rt_priority p->prio newpri cpupri
+ *
+ * -1 -1 (CPUPRI_INVALID)
+ *
+ * 99 0 (CPUPRI_NORMAL)
+ *
+ * 1 98 98 1
+ * ...
+ * 49 50 50 49
+ * 50 49 49 50
+ * ...
+ * 99 0 0 99
+ */
static int convert_prio(int prio)
{
int cpupri;

- if (prio == CPUPRI_INVALID)
- cpupri = CPUPRI_INVALID;
- else if (prio >= MAX_RT_PRIO)
- cpupri = CPUPRI_NORMAL;
- else
- cpupri = MAX_RT_PRIO - prio - 1;
+ switch (prio) {
+ case CPUPRI_INVALID:
+ cpupri = CPUPRI_INVALID; /* -1 */
+ break;
+
+ case 0...98:
+ cpupri = MAX_RT_PRIO-1 - prio; /* 1 ... 99 */
+ break;
+
+ case MAX_RT_PRIO-1:
+ cpupri = CPUPRI_NORMAL; /* 0 */
+ break;
+ }

return cpupri;
}
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -89,8 +89,8 @@ void init_rt_rq(struct rt_rq *rt_rq)
__set_bit(MAX_RT_PRIO, array->bitmap);

#if defined CONFIG_SMP
- rt_rq->highest_prio.curr = MAX_RT_PRIO;
- rt_rq->highest_prio.next = MAX_RT_PRIO;
+ rt_rq->highest_prio.curr = MAX_RT_PRIO-1;
+ rt_rq->highest_prio.next = MAX_RT_PRIO-1;
rt_rq->rt_nr_migratory = 0;
rt_rq->overloaded = 0;
plist_head_init(&rt_rq->pushable_tasks);
@@ -161,7 +161,7 @@ void init_tg_rt_entry(struct task_group
{
struct rq *rq = cpu_rq(cpu);

- rt_rq->highest_prio.curr = MAX_RT_PRIO;
+ rt_rq->highest_prio.curr = MAX_RT_PRIO-1;
rt_rq->rt_nr_boosted = 0;
rt_rq->rq = rq;
rt_rq->tg = tg;
@@ -393,8 +393,9 @@ static void dequeue_pushable_task(struct
p = plist_first_entry(&rq->rt.pushable_tasks,
struct task_struct, pushable_tasks);
rq->rt.highest_prio.next = p->prio;
- } else
- rq->rt.highest_prio.next = MAX_RT_PRIO;
+ } else {
+ rq->rt.highest_prio.next = MAX_RT_PRIO-1;
+ }
}

#else
@@ -1147,8 +1148,9 @@ dec_rt_prio(struct rt_rq *rt_rq, int pri
sched_find_first_bit(array->bitmap);
}

- } else
- rt_rq->highest_prio.curr = MAX_RT_PRIO;
+ } else {
+ rt_rq->highest_prio.curr = MAX_RT_PRIO-1;
+ }

dec_rt_prio_smp(rt_rq, prio, prev_prio);
}
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