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>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index fe19016..79ac078 100644 (file)
--- 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);