sched/cpupri: Remove the vec->lock

[mv-sheeva.git] / kernel / sched_cpupri.c

diff --git a/kernel/sched_cpupri.c b/kernel/sched_cpupri.c
index 2722dc1b41383fa6f8108802315cbc82c3c1e814..7761a2669fff717ee8afb64841639a0259fff015 100644 (file)
--- a/kernel/sched_cpupri.c
+++ b/kernel/sched_cpupri.c
@@ -47,9 +47,6 @@ static int convert_prio(int prio)
        return cpupri;
 }
 
-#define for_each_cpupri_active(array, idx)                    \
-       for_each_set_bit(idx, array, CPUPRI_NR_PRIORITIES)
-
 /**
  * cpupri_find - find the best (lowest-pri) CPU in the system
  * @cp: The cpupri context
@@ -71,11 +68,33 @@ int cpupri_find(struct cpupri *cp, struct task_struct *p,
        int                  idx      = 0;
        int                  task_pri = convert_prio(p->prio);
 
-       for_each_cpupri_active(cp->pri_active, idx) {
+       if (task_pri >= MAX_RT_PRIO)
+               return 0;
+
+       for (idx = 0; idx < task_pri; idx++) {
                struct cpupri_vec *vec  = &cp->pri_to_cpu[idx];
 
-               if (idx >= task_pri)
-                       break;
+               if (!atomic_read(&(vec)->count))
+                       continue;
+               /*
+                * When looking at the vector, we need to read the counter,
+                * do a memory barrier, then read the mask.
+                *
+                * Note: This is still all racey, but we can deal with it.
+                *  Ideally, we only want to look at masks that are set.
+                *
+                *  If a mask is not set, then the only thing wrong is that we
+                *  did a little more work than necessary.
+                *
+                *  If we read a zero count but the mask is set, because of the
+                *  memory barriers, that can only happen when the highest prio
+                *  task for a run queue has left the run queue, in which case,
+                *  it will be followed by a pull. If the task we are processing
+                *  fails to find a proper place to go, that pull request will
+                *  pull this task if the run queue is running at a lower
+                *  priority.
+                */
+               smp_rmb();
 
                if (cpumask_any_and(&p->cpus_allowed, vec->mask) >= nr_cpu_ids)
                        continue;
@@ -115,7 +134,6 @@ void cpupri_set(struct cpupri *cp, int cpu, int newpri)
 {
        int                 *currpri = &cp->cpu_to_pri[cpu];
        int                  oldpri  = *currpri;
-       unsigned long        flags;
 
        newpri = convert_prio(newpri);
 
@@ -134,26 +152,25 @@ void cpupri_set(struct cpupri *cp, int cpu, int newpri)
        if (likely(newpri != CPUPRI_INVALID)) {
                struct cpupri_vec *vec = &cp->pri_to_cpu[newpri];
 
-               raw_spin_lock_irqsave(&vec->lock, flags);
-
                cpumask_set_cpu(cpu, vec->mask);
-               vec->count++;
-               if (vec->count == 1)
-                       set_bit(newpri, cp->pri_active);
-
-               raw_spin_unlock_irqrestore(&vec->lock, flags);
+               /*
+                * When adding a new vector, we update the mask first,
+                * do a write memory barrier, and then update the count, to
+                * make sure the vector is visible when count is set.
+                */
+               smp_wmb();
+               atomic_inc(&(vec)->count);
        }
        if (likely(oldpri != CPUPRI_INVALID)) {
                struct cpupri_vec *vec  = &cp->pri_to_cpu[oldpri];
 
-               raw_spin_lock_irqsave(&vec->lock, flags);
-
-               vec->count--;
-               if (!vec->count)
-                       clear_bit(oldpri, cp->pri_active);
+               /*
+                * When removing from the vector, we decrement the counter first
+                * do a memory barrier and then clear the mask.
+                */
+               atomic_dec(&(vec)->count);
+               smp_wmb();
                cpumask_clear_cpu(cpu, vec->mask);
-
-               raw_spin_unlock_irqrestore(&vec->lock, flags);
        }
 
        *currpri = newpri;
@@ -175,8 +192,7 @@ int cpupri_init(struct cpupri *cp)
        for (i = 0; i < CPUPRI_NR_PRIORITIES; i++) {
                struct cpupri_vec *vec = &cp->pri_to_cpu[i];
 
-               raw_spin_lock_init(&vec->lock);
-               vec->count = 0;
+               atomic_set(&vec->count, 0);
                if (!zalloc_cpumask_var(&vec->mask, GFP_KERNEL))
                        goto cleanup;
        }