From: Andrew Theurer <habanero@us.ibm.com>
Fix can_migrate to allow aggressive steal for idle cpus. This -was- in
mainline, but I believe sched_domains kind of blasted it outta there. IMO,
it's a no brainer for an idle cpu (with all that cache going to waste) to
be granted to steal a task. The one enhancement I have made was to make
sure the whole cpu was idle.
Signed-off-by: <habanero@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/kernel/sched.c | 50 ++++++++++++++++++++++++++-----------------------
1 files changed, 27 insertions(+), 23 deletions(-)
diff -puN kernel/sched.c~sched-can_migrate-exception-for-idle-cpus kernel/sched.c
--- 25/kernel/sched.c~sched-can_migrate-exception-for-idle-cpus 2004-12-03 20:56:29.866219832 -0800
+++ 25-akpm/kernel/sched.c 2004-12-03 20:56:29.874218616 -0800
@@ -456,6 +456,22 @@ static inline void rq_unlock(runqueue_t
spin_unlock_irq(&rq->lock);
}
+#ifdef CONFIG_SCHED_SMT
+static int cpu_and_siblings_are_idle(int cpu)
+{
+ int sib;
+ for_each_cpu_mask(sib, cpu_sibling_map[cpu]) {
+ if (idle_cpu(sib))
+ continue;
+ return 0;
+ }
+
+ return 1;
+}
+#else
+#define cpu_and_siblings_are_idle(A) idle_cpu(A)
+#endif
+
#ifdef CONFIG_SCHEDSTATS
/*
* Called when a process is dequeued from the active array and given
@@ -1669,13 +1685,18 @@ int can_migrate_task(task_t *p, runqueue
if (!cpu_isset(this_cpu, p->cpus_allowed))
return 0;
- /* Aggressive migration if we've failed balancing */
- if (idle == NEWLY_IDLE ||
- sd->nr_balance_failed < sd->cache_nice_tries) {
- if (task_hot(p, rq->timestamp_last_tick, sd))
- return 0;
- }
+ /*
+ * Aggressive migration if:
+ * 1) the [whole] cpu is idle, or
+ * 2) too many balance attempts have failed.
+ */
+ if (cpu_and_siblings_are_idle(this_cpu) || \
+ sd->nr_balance_failed > sd->cache_nice_tries)
+ return 1;
+
+ if (task_hot(p, rq->timestamp_last_tick, sd))
+ return 0;
return 1;
}
@@ -2090,23 +2111,6 @@ static inline void idle_balance(int this
}
}
-#ifdef CONFIG_SCHED_SMT
-static int cpu_and_siblings_are_idle(int cpu)
-{
- int sib;
- for_each_cpu_mask(sib, cpu_sibling_map[cpu]) {
- if (idle_cpu(sib))
- continue;
- return 0;
- }
-
- return 1;
-}
-#else
-#define cpu_and_siblings_are_idle(A) idle_cpu(A)
-#endif
-
-
/*
* active_load_balance is run by migration threads. It pushes running tasks
* off the busiest CPU onto idle CPUs. It requires at least 1 task to be
_