[sched, patch] better wake-balancing, #2

Ingo Molnar
2005-07-29T15:02:50Z

* Ingo Molnar <mingo@elte.hu> wrote:

> another approach would be the patch below, to do wakeup-balancing only
> if the wakeup CPU or the task CPU is idle.

there's an even simpler way: only do wakeup-balancing if this_cpu is
idle. (tbench results are still OK, and other workloads improved.)

Ingo

--------
do wakeup-balancing only if the wakeup-CPU is idle.

this prevents excessive wakeup-balancing while the system is highly
loaded, but helps spread out the workload on partly idle systems.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/sched.c | 6 ++++++
1 files changed, 6 insertions(+)

Index: linux-sched-curr/kernel/sched.c
===================================================================
--- linux-sched-curr.orig/kernel/sched.c
+++ linux-sched-curr/kernel/sched.c
@@ -1253,7 +1253,13 @@ static int try_to_wake_up(task_t *p, uns
if (unlikely(task_running(rq, p)))
goto out_activate;

+ /*
+ * Only do wakeup-balancing (== potentially migrate the task)
+ * if this CPU is idle:
+ */
new_cpu = cpu;
+ if (!idle_cpu(this_cpu))
+ goto out_set_cpu;

schedstat_inc(rq, ttwu_cnt);
if (cpu == this_cpu) {