sched: RT-balance, optimize
We can cheaply track the number of bits set in the cpumask for the lowest
priority CPUs. Therefore, compute the mask's weight and use it to skip
the optimal domain search logic when there is only one CPU available.
Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 72c8132..52d88f1 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -303,7 +303,7 @@
int cpu;
cpumask_t *valid_mask = &__get_cpu_var(valid_cpu_mask);
int lowest_prio = -1;
- int ret = 0;
+ int count = 0;
cpus_clear(*lowest_mask);
cpus_and(*valid_mask, cpu_online_map, task->cpus_allowed);
@@ -316,7 +316,7 @@
/* We look for lowest RT prio or non-rt CPU */
if (rq->rt.highest_prio >= MAX_RT_PRIO) {
- if (ret)
+ if (count)
cpus_clear(*lowest_mask);
cpu_set(rq->cpu, *lowest_mask);
return 1;
@@ -328,14 +328,17 @@
if (rq->rt.highest_prio > lowest_prio) {
/* new low - clear old data */
lowest_prio = rq->rt.highest_prio;
- cpus_clear(*lowest_mask);
+ if (count) {
+ cpus_clear(*lowest_mask);
+ count = 0;
+ }
}
cpu_set(rq->cpu, *lowest_mask);
- ret = 1;
+ count++;
}
}
- return ret;
+ return count;
}
static inline int pick_optimal_cpu(int this_cpu, cpumask_t *mask)
@@ -359,9 +362,17 @@
cpumask_t *lowest_mask = &__get_cpu_var(local_cpu_mask);
int this_cpu = smp_processor_id();
int cpu = task_cpu(task);
+ int count = find_lowest_cpus(task, lowest_mask);
- if (!find_lowest_cpus(task, lowest_mask))
- return -1;
+ if (!count)
+ return -1; /* No targets found */
+
+ /*
+ * There is no sense in performing an optimal search if only one
+ * target is found.
+ */
+ if (count == 1)
+ return first_cpu(*lowest_mask);
/*
* At this point we have built a mask of cpus representing the
