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Subject[PATCH 55/63] sched: numa: Avoid migrating tasks that are placed on their preferred node
Date
From: Peter Zijlstra <peterz@infradead.org>

(This changelog needs more work, it's currently inaccurate and it's not
clear at exactly what point rt > env->fbq_type is true for the logic to
kick in)

This patch classifies scheduler domains and runqueues into FBQ (cannot
guess what this expands to) types which are one of

regular: There are tasks running that do not care about their NUMA
placement

remote: There are tasks running that care about their placement but are
currently running on a node remote to their ideal placement

all: No distinction

To implement this the patch tracks the number of tasks that are optimally
NUMA placed (rq->nr_preferred_running) and the number of tasks running that
care about their placement (nr_numa_running). The load balancer uses this
information to avoid migrating idea placed NUMA tasks as long as better
options for load balancing exists.

Not-signed-off-by: Peter Zijlstra
---
kernel/sched/core.c | 29 ++++++++++++
kernel/sched/fair.c | 128 ++++++++++++++++++++++++++++++++++++++++++++++-----
kernel/sched/sched.h | 5 ++
3 files changed, 150 insertions(+), 12 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 336a8ba..7abbae9 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4485,6 +4485,35 @@ int migrate_task_to(struct task_struct *p, int target_cpu)

return stop_one_cpu(curr_cpu, migration_cpu_stop, &arg);
}
+
+/*
+ * Requeue a task on a given node and accurately track the number of NUMA
+ * tasks on the runqueues
+ */
+void sched_setnuma(struct task_struct *p, int nid)
+{
+ struct rq *rq;
+ unsigned long flags;
+ bool on_rq, running;
+
+ rq = task_rq_lock(p, &flags);
+ on_rq = p->on_rq;
+ running = task_current(rq, p);
+
+ if (on_rq)
+ dequeue_task(rq, p, 0);
+ if (running)
+ p->sched_class->put_prev_task(rq, p);
+
+ p->numa_preferred_nid = nid;
+ p->numa_migrate_seq = 1;
+
+ if (running)
+ p->sched_class->set_curr_task(rq);
+ if (on_rq)
+ enqueue_task(rq, p, 0);
+ task_rq_unlock(rq, p, &flags);
+}
#endif

/*
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f232be6..83c6e69 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -888,6 +888,18 @@ static unsigned int task_scan_max(struct task_struct *p)
*/
unsigned int sysctl_numa_balancing_settle_count __read_mostly = 4;

+static void account_numa_enqueue(struct rq *rq, struct task_struct *p)
+{
+ rq->nr_numa_running += (p->numa_preferred_nid != -1);
+ rq->nr_preferred_running += (p->numa_preferred_nid == task_node(p));
+}
+
+static void account_numa_dequeue(struct rq *rq, struct task_struct *p)
+{
+ rq->nr_numa_running -= (p->numa_preferred_nid != -1);
+ rq->nr_preferred_running -= (p->numa_preferred_nid == task_node(p));
+}
+
struct numa_group {
atomic_t refcount;

@@ -1227,6 +1239,8 @@ static int task_numa_migrate(struct task_struct *p)
if (env.best_cpu == -1)
return -EAGAIN;

+ sched_setnuma(p, env.dst_nid);
+
if (env.best_task == NULL) {
int ret = migrate_task_to(p, env.best_cpu);
return ret;
@@ -1342,8 +1356,7 @@ static void task_numa_placement(struct task_struct *p)
/* Preferred node as the node with the most faults */
if (max_faults && max_nid != p->numa_preferred_nid) {
/* Update the preferred nid and migrate task if possible */
- p->numa_preferred_nid = max_nid;
- p->numa_migrate_seq = 1;
+ sched_setnuma(p, max_nid);
numa_migrate_preferred(p);
}
}
@@ -1741,6 +1754,14 @@ void task_tick_numa(struct rq *rq, struct task_struct *curr)
static void task_tick_numa(struct rq *rq, struct task_struct *curr)
{
}
+
+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)
+{
+}
#endif /* CONFIG_NUMA_BALANCING */

static void
@@ -1750,8 +1771,12 @@ account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
if (!parent_entity(se))
update_load_add(&rq_of(cfs_rq)->load, se->load.weight);
#ifdef CONFIG_SMP
- if (entity_is_task(se))
- list_add(&se->group_node, &rq_of(cfs_rq)->cfs_tasks);
+ if (entity_is_task(se)) {
+ struct rq *rq = rq_of(cfs_rq);
+
+ account_numa_enqueue(rq, task_of(se));
+ list_add(&se->group_node, &rq->cfs_tasks);
+ }
#endif
cfs_rq->nr_running++;
}
@@ -1762,8 +1787,10 @@ account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
update_load_sub(&cfs_rq->load, se->load.weight);
if (!parent_entity(se))
update_load_sub(&rq_of(cfs_rq)->load, se->load.weight);
- if (entity_is_task(se))
+ if (entity_is_task(se)) {
+ account_numa_dequeue(rq_of(cfs_rq), task_of(se));
list_del_init(&se->group_node);
+ }
cfs_rq->nr_running--;
}

@@ -4558,6 +4585,8 @@ static bool yield_to_task_fair(struct rq *rq, struct task_struct *p, bool preemp

static unsigned long __read_mostly max_load_balance_interval = HZ/10;

+enum fbq_type { regular, remote, all };
+
#define LBF_ALL_PINNED 0x01
#define LBF_NEED_BREAK 0x02
#define LBF_DST_PINNED 0x04
@@ -4584,6 +4613,8 @@ struct lb_env {
unsigned int loop;
unsigned int loop_break;
unsigned int loop_max;
+
+ enum fbq_type fbq_type;
};

/*
@@ -5049,6 +5080,10 @@ struct sg_lb_stats {
unsigned int group_weight;
int group_imb; /* Is there an imbalance in the group ? */
int group_has_capacity; /* Is there extra capacity in the group? */
+#ifdef CONFIG_NUMA_BALANCING
+ unsigned int nr_numa_running;
+ unsigned int nr_preferred_running;
+#endif
};

/*
@@ -5340,6 +5375,10 @@ static inline void update_sg_lb_stats(struct lb_env *env,

sgs->group_load += load;
sgs->sum_nr_running += nr_running;
+#ifdef CONFIG_NUMA_BALANCING
+ sgs->nr_numa_running += rq->nr_numa_running;
+ sgs->nr_preferred_running += rq->nr_preferred_running;
+#endif
sgs->sum_weighted_load += weighted_cpuload(i);
if (idle_cpu(i))
sgs->idle_cpus++;
@@ -5414,14 +5453,43 @@ static bool update_sd_pick_busiest(struct lb_env *env,
return false;
}

+#ifdef CONFIG_NUMA_BALANCING
+static inline enum fbq_type fbq_classify_group(struct sg_lb_stats *sgs)
+{
+ if (sgs->sum_nr_running > sgs->nr_numa_running)
+ return regular;
+ if (sgs->sum_nr_running > sgs->nr_preferred_running)
+ return remote;
+ return all;
+}
+
+static inline enum fbq_type fbq_classify_rq(struct rq *rq)
+{
+ if (rq->nr_running > rq->nr_numa_running)
+ return regular;
+ if (rq->nr_running > rq->nr_preferred_running)
+ return remote;
+ return all;
+}
+#else
+static inline enum fbq_type fbq_classify_group(struct sg_lb_stats *sgs)
+{
+ return all;
+}
+
+static inline enum fbq_type fbq_classify_rq(struct rq *rq)
+{
+ return regular;
+}
+#endif /* CONFIG_NUMA_BALANCING */
+
/**
* update_sd_lb_stats - Update sched_domain's statistics for load balancing.
* @env: The load balancing environment.
* @balance: Should we balance.
* @sds: variable to hold the statistics for this sched_domain.
*/
-static inline void update_sd_lb_stats(struct lb_env *env,
- struct sd_lb_stats *sds)
+static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sds)
{
struct sched_domain *child = env->sd->child;
struct sched_group *sg = env->sd->groups;
@@ -5471,6 +5539,9 @@ static inline void update_sd_lb_stats(struct lb_env *env,

sg = sg->next;
} while (sg != env->sd->groups);
+
+ if (env->sd->flags & SD_NUMA)
+ env->fbq_type = fbq_classify_group(&sds->busiest_stat);
}

/**
@@ -5773,15 +5844,47 @@ static struct rq *find_busiest_queue(struct lb_env *env,
int i;

for_each_cpu_and(i, sched_group_cpus(group), env->cpus) {
- unsigned long power = power_of(i);
- unsigned long capacity = DIV_ROUND_CLOSEST(power,
- SCHED_POWER_SCALE);
- unsigned long wl;
+ unsigned long power, capacity, wl;
+ enum fbq_type rt;

+ rq = cpu_rq(i);
+ rt = fbq_classify_rq(rq);
+
+#ifdef CONFIG_NUMA_BALANCING
+ trace_printk("group(%d:%pc) rq(%d): wl: %lu nr: %d nrn: %d nrp: %d gt:%d rt:%d\n",
+ env->sd->level, sched_group_cpus(group), i,
+ weighted_cpuload(i), rq->nr_running,
+ rq->nr_numa_running, rq->nr_preferred_running,
+ env->fbq_type, rt);
+#endif
+
+ /*
+ * We classify groups/runqueues into three groups:
+ * - regular: there are !numa tasks
+ * - remote: there are numa tasks that run on the 'wrong' node
+ * - all: there is no distinction
+ *
+ * In order to avoid migrating ideally placed numa tasks,
+ * ignore those when there's better options.
+ *
+ * If we ignore the actual busiest queue to migrate another
+ * task, the next balance pass can still reduce the busiest
+ * queue by moving tasks around inside the node.
+ *
+ * If we cannot move enough load due to this classification
+ * the next pass will adjust the group classification and
+ * allow migration of more tasks.
+ *
+ * Both cases only affect the total convergence complexity.
+ */
+ if (rt > env->fbq_type)
+ continue;
+
+ power = power_of(i);
+ capacity = DIV_ROUND_CLOSEST(power, SCHED_POWER_SCALE);
if (!capacity)
capacity = fix_small_capacity(env->sd, group);

- rq = cpu_rq(i);
wl = weighted_cpuload(i);

/*
@@ -5893,6 +5996,7 @@ static int load_balance(int this_cpu, struct rq *this_rq,
.idle = idle,
.loop_break = sched_nr_migrate_break,
.cpus = cpus,
+ .fbq_type = all,
};

/*
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 657472d..22c470c 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -407,6 +407,10 @@ struct rq {
* remote CPUs use both these fields when doing load calculation.
*/
unsigned int nr_running;
+#ifdef CONFIG_NUMA_BALANCING
+ unsigned int nr_numa_running;
+ unsigned int nr_preferred_running;
+#endif
#define CPU_LOAD_IDX_MAX 5
unsigned long cpu_load[CPU_LOAD_IDX_MAX];
unsigned long last_load_update_tick;
@@ -555,6 +559,7 @@ static inline u64 rq_clock_task(struct rq *rq)
}

#ifdef CONFIG_NUMA_BALANCING
+extern void sched_setnuma(struct task_struct *p, int node);
extern int migrate_task_to(struct task_struct *p, int cpu);
extern int migrate_swap(struct task_struct *, struct task_struct *);
#endif /* CONFIG_NUMA_BALANCING */
--
1.8.1.4


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