Commit 5969fe06 authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
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[PATCH] sched: HT optimisation



If an idle sibling of an HT queue encounters a busy sibling, then make
higher level load balancing of the non-idle variety.

Performance of multiprocessor HT systems with low numbers of tasks
(generally < number of virtual CPUs) can be significantly worse than the
exact same workloads when running in non-HT mode.  The reason is largely
due to poor scheduling behaviour.

This patch improves the situation, making the performance gap far less
significant on one problematic test case (tbench).
Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
Acked-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent e17224bf
......@@ -1906,7 +1906,7 @@ 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;
......@@ -1931,6 +1931,9 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
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);
......@@ -2074,10 +2077,14 @@ static int load_balance(int this_cpu, runqueue_t *this_rq,
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;
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;
......@@ -2150,6 +2157,8 @@ static int load_balance(int this_cpu, runqueue_t *this_rq,
sd->balance_interval *= 2;
}
if (!nr_moved && !sd_idle && sd->flags & SD_SHARE_CPUPOWER)
return -1;
return nr_moved;
out_balanced:
......@@ -2161,6 +2170,8 @@ out_balanced:
(sd->balance_interval < sd->max_interval))
sd->balance_interval *= 2;
if (!sd_idle && sd->flags & SD_SHARE_CPUPOWER)
return -1;
return 0;
}
......@@ -2178,9 +2189,13 @@ static int load_balance_newidle(int this_cpu, runqueue_t *this_rq,
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;
......@@ -2205,15 +2220,19 @@ static int load_balance_newidle(int this_cpu, runqueue_t *this_rq,
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;
}
......@@ -2338,7 +2357,10 @@ static void rebalance_tick(int this_cpu, runqueue_t *this_rq,
if (j - sd->last_balance >= interval) {
if (load_balance(this_cpu, this_rq, sd, idle)) {
/* We've pulled tasks over so no longer idle */
/* We've pulled tasks over so either we're no
* longer idle, or one of our SMT siblings is
* not idle.
*/
idle = NOT_IDLE;
}
sd->last_balance += interval;
......
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