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Subject[tip:sched/core] sched/numa: Implement NUMA node level wake_affine()
Commit-ID:  3fed382b46baac83703130fe4cd3d9147f427fb9
Gitweb: http://git.kernel.org/tip/3fed382b46baac83703130fe4cd3d9147f427fb9
Author: Rik van Riel <riel@redhat.com>
AuthorDate: Fri, 23 Jun 2017 12:55:29 -0400
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Sat, 24 Jun 2017 08:57:52 +0200

sched/numa: Implement NUMA node level wake_affine()

Since select_idle_sibling() can place a task anywhere on a socket,
comparing loads between individual CPU cores makes no real sense
for deciding whether to do an affine wakeup across sockets, either.

Instead, compare the load between the sockets in a similar way the
load balancer and the numa balancing code do.

Signed-off-by: Rik van Riel <riel@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: jhladky@redhat.com
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/20170623165530.22514-4-riel@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/sched/fair.c | 130 ++++++++++++++++++++++++++++------------------------
1 file changed, 71 insertions(+), 59 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index fe19016..79ac078 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2586,6 +2586,60 @@ void task_tick_numa(struct rq *rq, struct task_struct *curr)
}
}
}
+
+/*
+ * Can a task be moved from prev_cpu to this_cpu without causing a load
+ * imbalance that would trigger the load balancer?
+ */
+static inline bool numa_wake_affine(struct sched_domain *sd,
+ struct task_struct *p, int this_cpu,
+ int prev_cpu, int sync)
+{
+ struct numa_stats prev_load, this_load;
+ s64 this_eff_load, prev_eff_load;
+
+ update_numa_stats(&prev_load, cpu_to_node(prev_cpu));
+ update_numa_stats(&this_load, cpu_to_node(this_cpu));
+
+ /*
+ * If sync wakeup then subtract the (maximum possible)
+ * effect of the currently running task from the load
+ * of the current CPU:
+ */
+ if (sync) {
+ unsigned long current_load = task_h_load(current);
+
+ if (this_load.load > current_load)
+ this_load.load -= current_load;
+ else
+ this_load.load = 0;
+ }
+
+ /*
+ * In low-load situations, where this_cpu's node is idle due to the
+ * sync cause above having dropped this_load.load to 0, move the task.
+ * Moving to an idle socket will not create a bad imbalance.
+ *
+ * Otherwise check if the nodes are near enough in load to allow this
+ * task to be woken on this_cpu's node.
+ */
+ if (this_load.load > 0) {
+ unsigned long task_load = task_h_load(p);
+
+ this_eff_load = 100;
+ this_eff_load *= prev_load.compute_capacity;
+
+ prev_eff_load = 100 + (sd->imbalance_pct - 100) / 2;
+ prev_eff_load *= this_load.compute_capacity;
+
+ this_eff_load *= this_load.load + task_load;
+ prev_eff_load *= prev_load.load - task_load;
+
+ return this_eff_load <= prev_eff_load;
+ }
+
+ return true;
+}
#else
static void task_tick_numa(struct rq *rq, struct task_struct *curr)
{
@@ -2598,6 +2652,13 @@ static inline void account_numa_enqueue(struct rq *rq, struct task_struct *p)
static inline void account_numa_dequeue(struct rq *rq, struct task_struct *p)
{
}
+
+static inline bool numa_wake_affine(struct sched_domain *sd,
+ struct task_struct *p, int this_cpu,
+ int prev_cpu, int sync)
+{
+ return true;
+}
#endif /* CONFIG_NUMA_BALANCING */

static void
@@ -5407,74 +5468,25 @@ static int wake_wide(struct task_struct *p)
static int wake_affine(struct sched_domain *sd, struct task_struct *p,
int prev_cpu, int sync)
{
- s64 this_load, load;
- s64 this_eff_load, prev_eff_load;
- int idx, this_cpu;
- struct task_group *tg;
- unsigned long weight;
- int balanced;
-
- idx = sd->wake_idx;
- this_cpu = smp_processor_id();
- load = source_load(prev_cpu, idx);
- this_load = target_load(this_cpu, idx);
+ int this_cpu = smp_processor_id();
+ bool affine = false;

/*
* Common case: CPUs are in the same socket, and select_idle_sibling()
* will do its thing regardless of what we return:
*/
if (cpus_share_cache(prev_cpu, this_cpu))
- return true;
-
- /*
- * If sync wakeup then subtract the (maximum possible)
- * effect of the currently running task from the load
- * of the current CPU:
- */
- if (sync) {
- tg = task_group(current);
- weight = current->se.avg.load_avg;
-
- this_load += effective_load(tg, this_cpu, -weight, -weight);
- load += effective_load(tg, prev_cpu, 0, -weight);
- }
-
- tg = task_group(p);
- weight = p->se.avg.load_avg;
-
- /*
- * In low-load situations, where prev_cpu is idle and this_cpu is idle
- * due to the sync cause above having dropped this_load to 0, we'll
- * always have an imbalance, but there's really nothing you can do
- * about that, so that's good too.
- *
- * Otherwise check if either cpus are near enough in load to allow this
- * task to be woken on this_cpu.
- */
- this_eff_load = 100;
- this_eff_load *= capacity_of(prev_cpu);
-
- prev_eff_load = 100 + (sd->imbalance_pct - 100) / 2;
- prev_eff_load *= capacity_of(this_cpu);
-
- if (this_load > 0) {
- this_eff_load *= this_load +
- effective_load(tg, this_cpu, weight, weight);
-
- prev_eff_load *= load + effective_load(tg, prev_cpu, 0, weight);
- }
-
- balanced = this_eff_load <= prev_eff_load;
+ affine = true;
+ else
+ affine = numa_wake_affine(sd, p, this_cpu, prev_cpu, sync);

schedstat_inc(p->se.statistics.nr_wakeups_affine_attempts);
+ if (affine) {
+ schedstat_inc(sd->ttwu_move_affine);
+ schedstat_inc(p->se.statistics.nr_wakeups_affine);
+ }

- if (!balanced)
- return 0;
-
- schedstat_inc(sd->ttwu_move_affine);
- schedstat_inc(p->se.statistics.nr_wakeups_affine);
-
- return 1;
+ return affine;
}

static inline int task_util(struct task_struct *p);
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