From: "Martin J. Bligh" <mbligh@aracnet.com>
Fix a minor nit with the find_busiest_group code. No functional change,
but makes the code simpler and clearer. This patch does two things ...
adds some more expansive comments, and removes this if clause:
if (*imbalance < SCHED_LOAD_SCALE
&& max_load - this_load > SCHED_LOAD_SCALE)
*imbalance = SCHED_LOAD_SCALE;
If we remove the scaling factor, we're basically conditionally doing:
if (*imbalance < 1)
*imbalance = 1;
Which is pointless, as the very next thing we do is to remove the scaling
factor, rounding up to the nearest integer as we do:
*imbalance = (*imbalance + SCHED_LOAD_SCALE - 1) >> SCHED_LOAD_SHIFT;
Thus the if statement is redundant, and only makes the code harder to read
;-)
---
25-akpm/kernel/sched.c | 13 +++++++++----
1 files changed, 9 insertions(+), 4 deletions(-)
diff -puN kernel/sched.c~sched-find_busiest_group-clarification kernel/sched.c
--- 25/kernel/sched.c~sched-find_busiest_group-clarification Wed Feb 11 18:35:45 2004
+++ 25-akpm/kernel/sched.c Wed Feb 11 18:35:45 2004
@@ -1442,11 +1442,16 @@ nextgroup:
if (idle == NOT_IDLE && 100*max_load <= domain->imbalance_pct*this_load)
goto out_balanced;
- /* Take the minimum possible imbalance. */
+ /*
+ * We're trying to get all the cpus to the average_load, so we don't
+ * want to push ourselves above the average load, nor do we wish to
+ * reduce the max loaded cpu below the average load, as either of these
+ * actions would just result in more rebalancing later, and ping-pong
+ * tasks around. Thus we look for the minimum possible imbalance.
+ */
*imbalance = min(max_load - avg_load, avg_load - this_load);
- if (*imbalance < SCHED_LOAD_SCALE
- && max_load - this_load > SCHED_LOAD_SCALE)
- *imbalance = SCHED_LOAD_SCALE;
+
+ /* Get rid of the scaling factor now, rounding *up* as we divide */
*imbalance = (*imbalance + SCHED_LOAD_SCALE - 1) >> SCHED_LOAD_SHIFT;
if (*imbalance == 0) {
_