Siddha, Suresh B wrote:
Jack Steiner brought this issue at my OLS talk.
Take a scenario where two tasks are pinned to two HT threads in a physical
package. Idle packages in the system will keep kicking migration_thread
on the busy package with out any success.
We will run into similar scenarios in the presence of CMP/NUMA.
Patch appended.
Hmm, I would have hoped the new "all_pinned" logic should have
handled this case properly. Are you actually seeing this happen?
I have a patch here which I still need to do more testing with,
which might help performance on HT systems.
I found that idle siblings could cause SMP and NUMA balancing to
be too aggressive in some cases.
Thanks,
Nick
--
SUSE Labs, Novell Inc.
If an idle sibling of an HT queue encounters a busy sibling, then
make higher level load balancing of the non-idle variety.
Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c 2005-07-29 19:30:39.000000000 +1000
+++ linux-2.6/kernel/sched.c 2005-07-29 19:35:01.000000000 +1000
@@ -1889,7 +1889,7 @@ out:
*/
static struct sched_group *
find_busiest_group(struct sched_domain *sd, int this_cpu,
- unsigned long *imbalance, enum idle_type idle)
+ unsigned long *imbalance, enum idle_type idle, int *sd_idle)
{
struct sched_group *busiest = NULL, *this = NULL, *group = sd->groups;
unsigned long max_load, avg_load, total_load, this_load, total_pwr;
@@ -1914,6 +1914,9 @@ find_busiest_group(struct sched_domain *
avg_load = 0;
for_each_cpu_mask(i, group->cpumask) {
+ if (*sd_idle && !idle_cpu(i))
+ *sd_idle = 0;
+
/* Bias balancing toward cpus of our domain */
if (local_group)
load = target_load(i, load_idx);
@@ -2057,11 +2060,15 @@ static int load_balance(int this_cpu, ru
unsigned long imbalance;
int nr_moved, all_pinned = 0;
int active_balance = 0;
+ int sd_idle = 0;
+
+ if (idle != NOT_IDLE && sd->flags & SD_SHARE_CPUPOWER)
+ sd_idle = 1;
spin_lock(&this_rq->lock);
schedstat_inc(sd, lb_cnt[idle]);
- group = find_busiest_group(sd, this_cpu, &imbalance, idle);
+ group = find_busiest_group(sd, this_cpu, &imbalance, idle, &sd_idle);
if (!group) {
schedstat_inc(sd, lb_nobusyg[idle]);
goto out_balanced;
@@ -2136,6 +2143,8 @@ static int load_balance(int this_cpu, ru
sd->balance_interval *= 2;
}
+ if (!nr_moved && !sd_idle && sd->flags & SD_SHARE_CPUPOWER)
+ return -1;
return nr_moved;
out_balanced:
@@ -2149,6 +2158,8 @@ out_balanced:
(sd->balance_interval < sd->max_interval))
sd->balance_interval *= 2;
+ if (!sd_idle && sd->flags & SD_SHARE_CPUPOWER)
+ return -1;
return 0;
}
@@ -2166,9 +2177,13 @@ static int load_balance_newidle(int this
runqueue_t *busiest = NULL;
unsigned long imbalance;
int nr_moved = 0;
+ int sd_idle = 0;
+ if (sd->flags & SD_SHARE_CPUPOWER)
+ sd_idle = 1;
+
schedstat_inc(sd, lb_cnt[NEWLY_IDLE]);
- group = find_busiest_group(sd, this_cpu, &imbalance, NEWLY_IDLE);
+ group = find_busiest_group(sd, this_cpu, &imbalance, NEWLY_IDLE,
&sd_idle);
if (!group) {
schedstat_inc(sd, lb_nobusyg[NEWLY_IDLE]);
goto out_balanced;
@@ -2193,15 +2208,19 @@ static int load_balance_newidle(int this
spin_unlock(&busiest->lock);
}
- if (!nr_moved)
+ if (!nr_moved) {
schedstat_inc(sd, lb_failed[NEWLY_IDLE]);
- else
+ if (!sd_idle && sd->flags & SD_SHARE_CPUPOWER)
+ return -1;
+ } else
sd->nr_balance_failed = 0;
return nr_moved;
out_balanced:
schedstat_inc(sd, lb_balanced[NEWLY_IDLE]);
+ if (!sd_idle && sd->flags & SD_SHARE_CPUPOWER)
+ return -1;
sd->nr_balance_failed = 0;
return 0;
}
