[PATCH 3/5] 2.6.0 sched migrate comment

Nick Piggin
2003-12-20T15:21:38Z

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Some comments were lost during minor surgery here...

[-- Attachment #2: sched-migrate-comment.patch --]
[-- Type: text/plain, Size: 2299 bytes --]

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;

_