[PATCH 3/5] 2.6.0 sched migrate comment

[Nick Piggin <piggin@cyberone.com.au>]

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Some comments were lost during minor surgery here...


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Some comments were lost during minor surgery here...


 linux-2.6-npiggin/kernel/sched.c |   42 +++++++++++++++++++++------------------
 1 files changed, 23 insertions(+), 19 deletions(-)

diff -puN kernel/sched.c~sched-migrate-comment kernel/sched.c
--- linux-2.6/kernel/sched.c~sched-migrate-comment	2003-12-04 13:01:06.000000000 +1100
+++ linux-2.6-npiggin/kernel/sched.c	2003-12-04 13:01:25.000000000 +1100
@@ -1179,25 +1179,34 @@ static inline void pull_task(runqueue_t 
 }
 
 /*
- * Previously:
- *
- * #define CAN_MIGRATE_TASK(p,rq,this_cpu)	\
- *	((!idle || (NS_TO_JIFFIES(now - (p)->timestamp) > \
- *		cache_decay_ticks)) && !task_running(rq, p) && \
- *			cpu_isset(this_cpu, (p)->cpus_allowed))
+ * can_migrate_task
+ * May task p from runqueue rq be migrated to this_cpu?
+ * idle: Is this_cpu idle
+ * Returns: 1 if p may be migrated, 0 otherwise.
  */
-
 static inline int
-can_migrate_task(task_t *tsk, runqueue_t *rq, int this_cpu, int idle)
+can_migrate_task(task_t *p, runqueue_t *rq, int this_cpu, int idle)
 {
-	unsigned long delta = sched_clock() - tsk->timestamp;
+	unsigned long delta;
+
+	/*
+	 * We do not migrate tasks that are:
+	 * 1) running (obviously), or
+	 * 2) cannot be migrated to this CPU due to cpus_allowed, or
+	 * 3) are cache-hot on their current CPU.
+	 */
 
-	if (!idle && (delta <= JIFFIES_TO_NS(cache_decay_ticks)))
+	if (task_running(rq, p))
 		return 0;
-	if (task_running(rq, tsk))
+
+	if (!cpu_isset(this_cpu, p->cpus_allowed))
 		return 0;
-	if (!cpu_isset(this_cpu, tsk->cpus_allowed))
+
+	/* Aggressive migration if we're idle */
+	delta = sched_clock() - p->timestamp;
+	if (!idle && (delta <= cache_decay_ticks))
 		return 0;
+
 	return 1;
 }
 
@@ -1259,13 +1268,6 @@ skip_bitmap:
 skip_queue:
 	tmp = list_entry(curr, task_t, run_list);
 
-	/*
-	 * We do not migrate tasks that are:
-	 * 1) running (obviously), or
-	 * 2) cannot be migrated to this CPU due to cpus_allowed, or
-	 * 3) are cache-hot on their current CPU.
-	 */
-
 	curr = curr->prev;
 
 	if (!can_migrate_task(tmp, busiest, this_cpu, idle)) {
@@ -1275,6 +1277,8 @@ skip_queue:
 		goto skip_bitmap;
 	}
 	pull_task(busiest, array, tmp, this_rq, this_cpu);
+
+	/* Only migrate 1 task if we're idle */
 	if (!idle && --imbalance) {
 		if (curr != head)
 			goto skip_queue;

_