Martin J. Bligh wrote:
Attached is a new patch to fix the excessive idle problem. This patch
takes a new approach to the problem as it was becoming obvious that
trying to alter the load balancing code to cope with biased load was
harder than it seemed.
This approach reverts to the old load values but weights them
according to tasks' bias_prio values. This means that any assumptions
by the load balancing code that the load generated by a single task is
SCHED_LOAD_SCALE will still hold. Then, in find_busiest_group(), the
imbalance is scaled back up to bias_prio scale so that move_tasks()
can move biased load rather than tasks.
OK, this one seems to fix the issue that I had, AFAICS. Congrats, and
thanks,
Terrific, thanks for testing.
Con,
Attached is a cleaned up version of this patch against 2.6.15-mm4 with
some (hopefully helpful) comments added.
Signed-off-by: Peter Williams <[email protected]>
--
Peter Williams [email protected]
"Learning, n. The kind of ignorance distinguishing the studious."
-- Ambrose Bierce
Index: MM-2.6.X/kernel/sched.c
===================================================================
--- MM-2.6.X.orig/kernel/sched.c 2006-01-15 09:54:27.000000000 +1100
+++ MM-2.6.X/kernel/sched.c 2006-01-15 10:50:11.000000000 +1100
@@ -681,6 +681,13 @@ static int effective_prio(task_t *p)
}
#ifdef CONFIG_SMP
+/*
+ * To aid in avoiding the subversion of "niceness" due to uneven distribution
+ * of tasks with abnormal "nice" values accross CPUs the contribution that
+ * each task makes to its run queue's load is weighted according to its
+ * scheduling class and "nice" value. The bias_prio field holds the value
+ * used to calculate the weight for each task.
+ */
static inline void set_bias_prio(task_t *p)
{
if (rt_task(p)) {
@@ -718,6 +725,18 @@ static inline void dec_nr_running(task_t
rq->nr_running--;
dec_prio_bias(rq, p);
}
+
+/* convert biased priority to scaled weighted load */
+static inline unsigned long weighted_load(unsigned long bias)
+{
+ return (bias * SCHED_LOAD_SCALE) / NICE_TO_BIAS_PRIO(0);
+}
+
+/* convert scaled weighted load to unscaled biased load */
+static inline unsigned long biased_load(unsigned long wload)
+{
+ return (wload * NICE_TO_BIAS_PRIO(0)) / SCHED_LOAD_SCALE;
+}
#else
static inline void set_bias_prio(task_t *p)
{
@@ -1011,7 +1030,8 @@ void kick_process(task_t *p)
}
/*
- * Return a low guess at the load of a migration-source cpu.
+ * Return a low guess at the load of a migration-source cpu weighted
+ * according to the scheduling class and "nice" value.
*
* We want to under-estimate the load of migration sources, to
* balance conservatively.
@@ -1019,7 +1039,7 @@ void kick_process(task_t *p)
static unsigned long source_load(int cpu, int type)
{
runqueue_t *rq = cpu_rq(cpu);
- unsigned long load_now = rq->prio_bias * SCHED_LOAD_SCALE;
+ unsigned long load_now = weighted_load(rq->prio_bias);
if (type == 0)
return load_now;
@@ -1028,12 +1048,13 @@ static unsigned long source_load(int cpu
}
/*
- * Return a high guess at the load of a migration-target cpu
+ * Return a high guess at the load of a migration-target cpu weighted
+ * according to the scheduling class and "nice" value.
*/
static inline unsigned long target_load(int cpu, int type)
{
runqueue_t *rq = cpu_rq(cpu);
- unsigned long load_now = rq->prio_bias * SCHED_LOAD_SCALE;
+ unsigned long load_now = weighted_load(rq->prio_bias);
if (type == 0)
return load_now;
@@ -1299,7 +1320,7 @@ static int try_to_wake_up(task_t *p, uns
* of the current CPU:
*/
if (sync)
- tl -= p->bias_prio * SCHED_LOAD_SCALE;
+ tl -= weighted_load(p->bias_prio);
if ((tl <= load &&
tl + target_load(cpu, idx) <= SCHED_LOAD_SCALE) ||
@@ -1903,9 +1924,9 @@ int can_migrate_task(task_t *p, runqueue
}
/*
- * move_tasks tries to move up to max_nr_move tasks from busiest to this_rq,
- * as part of a balancing operation within "domain". Returns the number of
- * tasks moved.
+ * move_tasks tries to move up to max_nr_move tasks and max_bias_move biased
+ * load from busiest to this_rq, as part of a balancing operation within
+ * "domain". Returns the number of tasks moved.
*
* Called with both runqueues locked.
*/
@@ -2134,8 +2155,11 @@ find_busiest_group(struct sched_domain *
return busiest;
}
- /* Get rid of the scaling factor, rounding down as we divide */
- *imbalance = *imbalance / SCHED_LOAD_SCALE;
+ /*
+ * Get rid of the scaling factor, rounding down as we divide and
+ * converting to biased load for use by move_tasks()
+ */
+ *imbalance = biased_load(*imbalance);
return busiest;
out_balanced:
@@ -2448,7 +2472,8 @@ static void rebalance_tick(int this_cpu,
struct sched_domain *sd;
int i;
- this_load = this_rq->prio_bias * SCHED_LOAD_SCALE;
+ /* weight load according to scheduling class and "nice" value */
+ this_load = weighted_load(this_rq->prio_bias);
/* Update our load */
for (i = 0; i < 3; i++) {
unsigned long new_load = this_load;
Index: MM-2.6.X/include/linux/sched.h
===================================================================
--- MM-2.6.X.orig/include/linux/sched.h 2006-01-15 09:54:27.000000000 +1100
+++ MM-2.6.X/include/linux/sched.h 2006-01-15 10:14:42.000000000 +1100
@@ -714,7 +714,7 @@ struct task_struct {
#endif
int prio, static_prio;
#ifdef CONFIG_SMP
- int bias_prio;
+ int bias_prio; /* load "weight" factor for load balancing purposes */
#endif
struct list_head run_list;
prio_array_t *array;
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
