From: Nick Piggin <nickpiggin@yahoo.com.au>
Make affine wakes and "passive load balancing" more conservative. Aggressive
affine wakeups were causing huge regressions in dbt3-pgsql on 8-way non NUMA
systems at OSDL's STP.
---
25-akpm/kernel/sched.c | 24 +++++++++++++++++-------
1 files changed, 17 insertions(+), 7 deletions(-)
diff -puN kernel/sched.c~sched-wakebalance-fixes kernel/sched.c
--- 25/kernel/sched.c~sched-wakebalance-fixes 2004-03-28 23:16:21.699105800 -0800
+++ 25-akpm/kernel/sched.c 2004-03-28 23:16:21.703105192 -0800
@@ -706,15 +706,26 @@ static int try_to_wake_up(task_t * p, un
if (unlikely(task_running(rq, p) || cpu_is_offline(this_cpu)))
goto out_activate;
- new_cpu = this_cpu; /* Wake to this CPU if we can */
+ new_cpu = cpu;
if (cpu == this_cpu || unlikely(!cpu_isset(this_cpu, p->cpus_allowed)))
goto out_set_cpu;
- /* Passive load balancing */
load = get_low_cpu_load(cpu);
- this_load = get_high_cpu_load(this_cpu) + SCHED_LOAD_SCALE;
- if (load > this_load)
+ this_load = get_high_cpu_load(this_cpu);
+
+ /* Don't pull the task off an idle CPU to a busy one */
+ if (load < SCHED_LOAD_SCALE/2 && this_load > SCHED_LOAD_SCALE/2)
+ goto out_set_cpu;
+
+ new_cpu = this_cpu; /* Wake to this CPU if we can */
+
+ /*
+ * Passive load balancing. If the queues are very out of balance
+ * we might as well balance here rather than the periodic load
+ * balancing.
+ */
+ if (load > this_load + SCHED_LOAD_SCALE*2)
goto out_set_cpu;
now = sched_clock();
@@ -726,7 +737,7 @@ static int try_to_wake_up(task_t * p, un
for_each_domain(this_cpu, sd) {
if (!(sd->flags & SD_WAKE_AFFINE))
break;
- if (now - p->timestamp < sd->cache_hot_time)
+ if (rq->timestamp_last_tick - p->timestamp < sd->cache_hot_time)
break;
if (cpu_isset(cpu, sd->span))
@@ -1264,8 +1275,7 @@ int can_migrate_task(task_t *p, runqueue
/* Aggressive migration if we've failed balancing */
if (idle == NEWLY_IDLE ||
sd->nr_balance_failed < sd->cache_nice_tries) {
- if ((rq->timestamp_last_tick - p->timestamp)
- < sd->cache_hot_time)
+ if (rq->timestamp_last_tick - p->timestamp < sd->cache_hot_time)
return 0;
}
_