But I was thinking more about the code that (in the original) handled
the case where the number of tasks to be moved was less than 1 but
more than 0 (i.e. the cases where "imbalance" would have been reduced
to zero when divided by SCHED_LOAD_SCALE). I think that I got that
part wrong and you can end up with a bias load to be moved which is
less than any of the bias_prio values for any queued tasks (in
circumstances where the original code would have rounded up to 1 and
caused a move). I think that the way to handle this problem is to
replace 1 with "average bias prio" within that logic. This would
guarantee at least one task with a bias_prio small enough to be moved.
I think that this analysis is a strong argument for my original patch
being the cause of the problem so I'll go ahead and generate a fix.
I'll try to have a patch available later this morning.
Attached is a patch that addresses this problem. Unlike the description
above it does not use "average bias prio" as that solution would be very
complicated. Instead it makes the assumption that NICE_TO_BIAS_PRIO(0)
is a "good enough" for this purpose as this is highly likely to be the
median bias prio and the median is probably better for this purpose than
the average.
Signed-off-by: Peter Williams <[email protected]>
Doesn't fix the perf issue.
M.
Peter
------------------------------------------------------------------------
Index: MM-2.6.X/kernel/sched.c
===================================================================
--- MM-2.6.X.orig/kernel/sched.c 2006-01-12 09:23:38.000000000 +1100
+++ MM-2.6.X/kernel/sched.c 2006-01-12 10:44:50.000000000 +1100
@@ -2116,11 +2116,11 @@ find_busiest_group(struct sched_domain *
(avg_load - this_load) * this->cpu_power)
/ SCHED_LOAD_SCALE;
- if (*imbalance < SCHED_LOAD_SCALE) {
+ if (*imbalance < NICE_TO_BIAS_PRIO(0) * SCHED_LOAD_SCALE) {
unsigned long pwr_now = 0, pwr_move = 0;
unsigned long tmp;
- if (max_load - this_load >= SCHED_LOAD_SCALE*2) {
+ if (max_load - this_load >= NICE_TO_BIAS_PRIO(0) * SCHED_LOAD_SCALE*2) {
*imbalance = NICE_TO_BIAS_PRIO(0);
return busiest;
}
-
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