[PATCH 02/19] sched/numa: Evaluate move once per node

Srikar Dronamraju
2018-06-04T10:06:08Z

task_numa_compare() helps choose the best cpu to move or swap the
selected task. To achieve this task_numa_compare() is called for every
cpu in the node. Currently it evaluates if the task can be moved/swapped
for each of the cpus. However the move evaluation is mostly independent
of the cpu. Evaluating the move logic once per node, provides scope for
simplifying task_numa_compare().

Testcase Time: Min Max Avg StdDev
numa01.sh Real: 440.65 941.32 758.98 189.17
numa01.sh Sys: 183.48 320.07 258.42 50.09
numa01.sh User: 37384.65 71818.14 60302.51 13798.96
numa02.sh Real: 61.24 65.35 62.49 1.49
numa02.sh Sys: 16.83 24.18 21.40 2.60
numa02.sh User: 5219.59 5356.34 5264.03 49.07
numa03.sh Real: 822.04 912.40 873.55 37.35
numa03.sh Sys: 118.80 140.94 132.90 7.60
numa03.sh User: 62485.19 70025.01 67208.33 2967.10
numa04.sh Real: 690.66 872.12 778.49 65.44
numa04.sh Sys: 459.26 563.03 494.03 42.39
numa04.sh User: 51116.44 70527.20 58849.44 8461.28
numa05.sh Real: 418.37 562.28 525.77 54.27
numa05.sh Sys: 299.45 481.00 392.49 64.27
numa05.sh User: 34115.09 41324.02 39105.30 2627.68

Testcase Time: Min Max Avg StdDev %Change
numa01.sh Real: 516.14 892.41 739.84 151.32 2.587%
numa01.sh Sys: 153.16 192.99 177.70 14.58 45.42%
numa01.sh User: 39821.04 69528.92 57193.87 10989.48 5.435%
numa02.sh Real: 60.91 62.35 61.58 0.63 1.477%
numa02.sh Sys: 16.47 26.16 21.20 3.85 0.943%
numa02.sh User: 5227.58 5309.61 5265.17 31.04 -0.02%
numa03.sh Real: 739.07 917.73 795.75 64.45 9.776%
numa03.sh Sys: 94.46 136.08 109.48 14.58 21.39%
numa03.sh User: 57478.56 72014.09 61764.48 5343.69 8.813%
numa04.sh Real: 442.61 715.43 530.31 96.12 46.79%
numa04.sh Sys: 224.90 348.63 285.61 48.83 72.97%
numa04.sh User: 35836.84 47522.47 40235.41 3985.26 46.26%
numa05.sh Real: 386.13 489.17 434.94 43.59 20.88%
numa05.sh Sys: 144.29 438.56 278.80 105.78 40.77%
numa05.sh User: 33255.86 36890.82 34879.31 1641.98 12.11%

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
---
kernel/sched/fair.c | 128 +++++++++++++++++++++++-----------------------------
1 file changed, 57 insertions(+), 71 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 79f574d..57d1ee8 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1541,9 +1541,8 @@ static bool load_too_imbalanced(long src_load, long dst_load,
* be exchanged with the source task
*/
static void task_numa_compare(struct task_numa_env *env,
- long taskimp, long groupimp)
+ long taskimp, long groupimp, bool move)
{
- struct rq *src_rq = cpu_rq(env->src_cpu);
struct rq *dst_rq = cpu_rq(env->dst_cpu);
struct task_struct *cur;
long src_load, dst_load;
@@ -1564,97 +1563,73 @@ static void task_numa_compare(struct task_numa_env *env,
if (cur == env->p)
goto unlock;

+ if (!cur) {
+ if (!move || imp <= env->best_imp)
+ goto unlock;
+ else
+ goto assign;
+ }
+
/*
* "imp" is the fault differential for the source task between the
* source and destination node. Calculate the total differential for
* the source task and potential destination task. The more negative
- * the value is, the more rmeote accesses that would be expected to
+ * the value is, the more remote accesses that would be expected to
* be incurred if the tasks were swapped.
*/
- if (cur) {
- /* Skip this swap candidate if cannot move to the source CPU: */
- if (!cpumask_test_cpu(env->src_cpu, &cur->cpus_allowed))
- goto unlock;
+ /* Skip this swap candidate if cannot move to the source cpu */
+ if (!cpumask_test_cpu(env->src_cpu, &cur->cpus_allowed))
+ goto unlock;

+ /*
+ * If dst and source tasks are in the same NUMA group, or not
+ * in any group then look only at task weights.
+ */
+ if (cur->numa_group == env->p->numa_group) {
+ imp = taskimp + task_weight(cur, env->src_nid, dist) -
+ task_weight(cur, env->dst_nid, dist);
/*
- * If dst and source tasks are in the same NUMA group, or not
- * in any group then look only at task weights.
+ * Add some hysteresis to prevent swapping the
+ * tasks within a group over tiny differences.
*/
- if (cur->numa_group == env->p->numa_group) {
- imp = taskimp + task_weight(cur, env->src_nid, dist) -
- task_weight(cur, env->dst_nid, dist);
- /*
- * Add some hysteresis to prevent swapping the
- * tasks within a group over tiny differences.
- */
- if (cur->numa_group)
- imp -= imp/16;
- } else {
- /*
- * Compare the group weights. If a task is all by
- * itself (not part of a group), use the task weight
- * instead.
- */
- if (cur->numa_group)
- imp += group_weight(cur, env->src_nid, dist) -
- group_weight(cur, env->dst_nid, dist);
- else
- imp += task_weight(cur, env->src_nid, dist) -
- task_weight(cur, env->dst_nid, dist);
- }
+ if (cur->numa_group)
+ imp -= imp / 16;
+ } else {
+ /*
+ * Compare the group weights. If a task is all by itself
+ * (not part of a group), use the task weight instead.
+ */
+ if (cur->numa_group && env->p->numa_group)
+ imp += group_weight(cur, env->src_nid, dist) -
+ group_weight(cur, env->dst_nid, dist);
+ else
+ imp += task_weight(cur, env->src_nid, dist) -
+ task_weight(cur, env->dst_nid, dist);
}

- if (imp <= env->best_imp && moveimp <= env->best_imp)
+ if (imp <= env->best_imp)
goto unlock;

- if (!cur) {
- /* Is there capacity at our destination? */
- if (env->src_stats.nr_running <= env->src_stats.task_capacity &&
- !env->dst_stats.has_free_capacity)
- goto unlock;
-
- goto balance;
- }
-
- /* Balance doesn't matter much if we're running a task per CPU: */
- if (imp > env->best_imp && src_rq->nr_running == 1 &&
- dst_rq->nr_running == 1)
+ if (move && moveimp > imp && moveimp > env->best_imp) {
+ imp = moveimp - 1;
+ cur = NULL;
goto assign;
+ }

/*
* In the overloaded case, try and keep the load balanced.
*/
-balance:
- load = task_h_load(env->p);
+ load = task_h_load(env->p) - task_h_load(cur);
+ if (!load)
+ goto assign;
+
dst_load = env->dst_stats.load + load;
src_load = env->src_stats.load - load;

- if (moveimp > imp && moveimp > env->best_imp) {
- /*
- * If the improvement from just moving env->p direction is
- * better than swapping tasks around, check if a move is
- * possible. Store a slightly smaller score than moveimp,
- * so an actually idle CPU will win.
- */
- if (!load_too_imbalanced(src_load, dst_load, env)) {
- imp = moveimp - 1;
- cur = NULL;
- goto assign;
- }
- }
-
- if (imp <= env->best_imp)
- goto unlock;
-
- if (cur) {
- load = task_h_load(cur);
- dst_load -= load;
- src_load += load;
- }
-
if (load_too_imbalanced(src_load, dst_load, env))
goto unlock;

+assign:
/*
* One idle CPU per node is evaluated for a task numa move.
* Call select_idle_sibling to maybe find a better one.
@@ -1670,7 +1645,6 @@ static void task_numa_compare(struct task_numa_env *env,
local_irq_enable();
}

-assign:
task_numa_assign(env, cur, imp);
unlock:
rcu_read_unlock();
@@ -1679,15 +1653,27 @@ static void task_numa_compare(struct task_numa_env *env,
static void task_numa_find_cpu(struct task_numa_env *env,
long taskimp, long groupimp)
{
+ long src_load, dst_load, load;
+ bool move = false;
int cpu;

+ load = task_h_load(env->p);
+ dst_load = env->dst_stats.load + load;
+ src_load = env->src_stats.load - load;
+
+ /*
+ * If the improvement from just moving env->p direction is better
+ * than swapping tasks around, check if a move is possible.
+ */
+ move = !load_too_imbalanced(src_load, dst_load, env);
+
for_each_cpu(cpu, cpumask_of_node(env->dst_nid)) {
/* Skip this CPU if the source task cannot migrate */
if (!cpumask_test_cpu(cpu, &env->p->cpus_allowed))
continue;

env->dst_cpu = cpu;
- task_numa_compare(env, taskimp, groupimp);
+ task_numa_compare(env, taskimp, groupimp, move);
}
}

--
1.8.3.1