[tip:sched/numa] sched: Implement home-node awareness

From: tip-bot for Peter Zijlstra
Date: Fri Sep 28 2012 - 04:00:51 EST

Commit-ID: fc2fbef0374693278a767a3d31ef18293e68f6be
Gitweb: http://git.kernel.org/tip/fc2fbef0374693278a767a3d31ef18293e68f6be
Author: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
AuthorDate: Sat, 3 Mar 2012 16:56:25 +0100
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 27 Sep 2012 17:04:44 +0200

sched: Implement home-node awareness

Implement home node preference in the scheduler's load-balancer.

This is done in four pieces:

- task_numa_hot(); make it harder to migrate tasks away from their
home-node, controlled using the NUMA_HOT feature flag.

- select_task_rq_fair(); prefer placing the task in their home-node,
controlled using the NUMA_BIAS feature flag.

- load_balance(); during the regular pull load-balance pass, try
pulling tasks that are on the wrong node first with a preference
of moving them nearer to their home-node through task_numa_hot(),
controlled through the NUMA_PULL feature flag.

- load_balance(); when the balancer finds no imbalance, introduce
some such that it still prefers to move tasks towards their
home-node, using active load-balance if needed, controlled through
the NUMA_PULL_BIAS feature flag.

In order to easily find off-node tasks, split the per-cpu task list
into two parts.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Paul Turner <pjt@xxxxxxxxxx>
Cc: Lee Schermerhorn <Lee.Schermerhorn@xxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/n/tip-g0gzzzjrvrzxl6kgwnil1e97@xxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
include/linux/sched.h | 1 +
kernel/sched/core.c | 21 ++++-
kernel/sched/debug.c | 3 +
kernel/sched/fair.c | 248 +++++++++++++++++++++++++++++++++++++++++++++--
kernel/sched/features.h | 8 ++
kernel/sched/sched.h | 16 +++
6 files changed, 286 insertions(+), 11 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index d28ff49..8755ef1 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -861,6 +861,7 @@ enum cpu_idle_type {
#define SD_ASYM_PACKING 0x0800 /* Place busy groups earlier in the domain */
#define SD_PREFER_SIBLING 0x1000 /* Prefer to place tasks in a sibling domain */
#define SD_OVERLAP 0x2000 /* sched_domains of this level overlap */
+#define SD_NUMA 0x4000 /* cross-node balancing */

extern int __weak arch_sd_sibiling_asym_packing(void);

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a64c43b..f7e7432 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5472,7 +5472,9 @@ static void destroy_sched_domains(struct sched_domain *sd, int cpu)
DEFINE_PER_CPU(struct sched_domain *, sd_llc);
DEFINE_PER_CPU(int, sd_llc_id);

-static void update_top_cache_domain(int cpu)
+DEFINE_PER_CPU(struct sched_domain *, sd_node);
+
+static void update_domain_cache(int cpu)
{
struct sched_domain *sd;
int id = cpu;
@@ -5515,6 +5517,15 @@ static void update_top_cache_domain(int cpu)

rcu_assign_pointer(per_cpu(sd_llc, cpu), sd);
per_cpu(sd_llc_id, cpu) = id;
+
+ for_each_domain(cpu, sd) {
+ if (cpumask_equal(sched_domain_span(sd),
+ cpumask_of_node(cpu_to_node(cpu))))
+ goto got_node;
+ }
+ sd = NULL;
+got_node:
+ rcu_assign_pointer(per_cpu(sd_node, cpu), sd);
}

/*
@@ -5557,7 +5568,7 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu)
rcu_assign_pointer(rq->sd, sd);
destroy_sched_domains(tmp, cpu);

- update_top_cache_domain(cpu);
+ update_domain_cache(cpu);
}

/* cpus with isolated domains */
@@ -6060,6 +6071,7 @@ sd_numa_init(struct sched_domain_topology_level *tl, int cpu)
| 0*SD_SHARE_PKG_RESOURCES
| 1*SD_SERIALIZE
| 0*SD_PREFER_SIBLING
+ | 1*SD_NUMA
| sd_local_flags(level)
,
.last_balance = jiffies,
@@ -6852,6 +6864,11 @@ void __init sched_init(void)
rq->avg_idle = 2*sysctl_sched_migration_cost;

INIT_LIST_HEAD(&rq->cfs_tasks);
+#ifdef CONFIG_SCHED_NUMA
+ INIT_LIST_HEAD(&rq->offnode_tasks);
+ rq->offnode_running = 0;
+ rq->offnode_weight = 0;
+#endif

rq_attach_root(rq, &def_root_domain);
#ifdef CONFIG_NO_HZ
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 6f79596..c9a5f75 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -132,6 +132,9 @@ print_task(struct seq_file *m, struct rq *rq, struct task_struct *p)
SEQ_printf(m, "%15Ld %15Ld %15Ld.%06ld %15Ld.%06ld %15Ld.%06ld",
0LL, 0LL, 0LL, 0L, 0LL, 0L, 0LL, 0L);
#endif
+#ifdef CONFIG_SCHED_NUMA
+ SEQ_printf(m, " %d/%d", p->node, cpu_to_node(task_cpu(p)));
+#endif
#ifdef CONFIG_CGROUP_SCHED
SEQ_printf(m, " %s", task_group_path(task_group(p)));
#endif
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index ffa10d6..29c4704 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -26,6 +26,7 @@
#include <linux/slab.h>
#include <linux/profile.h>
#include <linux/interrupt.h>
+#include <linux/random.h>

#include <trace/events/sched.h>

@@ -2667,6 +2668,35 @@ static int select_idle_sibling(struct task_struct *p, int target)
return target;
}

+#ifdef CONFIG_SCHED_NUMA
+static inline bool pick_numa_rand(int n)
+{
+ return !(get_random_int() % n);
+}
+
+/*
+ * Pick a random elegible CPU in the target node, hopefully faster
+ * than doing a least-loaded scan.
+ */
+static int numa_select_node_cpu(struct task_struct *p, int node)
+{
+ int weight = cpumask_weight(cpumask_of_node(node));
+ int i, cpu = -1;
+
+ for_each_cpu_and(i, cpumask_of_node(node), tsk_cpus_allowed(p)) {
+ if (cpu < 0 || pick_numa_rand(weight))
+ cpu = i;
+ }
+
+ return cpu;
+}
+#else
+static int numa_select_node_cpu(struct task_struct *p, int node)
+{
+ return -1;
+}
+#endif /* CONFIG_SCHED_NUMA */
+
/*
* sched_balance_self: balance the current task (running on cpu) in domains
* that have the 'flag' flag set. In practice, this is SD_BALANCE_FORK and
@@ -2687,6 +2717,7 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
int new_cpu = cpu;
int want_affine = 0;
int sync = wake_flags & WF_SYNC;
+ int node = tsk_home_node(p);

if (p->nr_cpus_allowed == 1)
return prev_cpu;
@@ -2698,6 +2729,33 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
}

rcu_read_lock();
+ if (sched_feat_numa(NUMA_BIAS) && node != -1) {
+ /*
+ * For fork,exec find the idlest cpu in the home-node.
+ */
+ if (sd_flag & (SD_BALANCE_FORK|SD_BALANCE_EXEC)) {
+ int node_cpu = numa_select_node_cpu(p, node);
+ if (node_cpu < 0)
+ goto find_sd;
+
+ new_cpu = cpu = node_cpu;
+ sd = per_cpu(sd_node, cpu);
+ goto pick_idlest;
+ }
+
+ /*
+ * For wake, pretend we were running in the home-node.
+ */
+ if (cpu_to_node(prev_cpu) != node) {
+ int node_cpu = numa_select_node_cpu(p, node);
+ if (node_cpu < 0)
+ goto find_sd;
+
+ prev_cpu = node_cpu;
+ }
+ }
+
+find_sd:
for_each_domain(cpu, tmp) {
if (!(tmp->flags & SD_LOAD_BALANCE))
continue;
@@ -2724,6 +2782,7 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
goto unlock;
}

+pick_idlest:
while (sd) {
int load_idx = sd->forkexec_idx;
struct sched_group *group;
@@ -3046,6 +3105,8 @@ struct lb_env {

unsigned int flags;

+ struct list_head *tasks;
+
unsigned int loop;
unsigned int loop_break;
unsigned int loop_max;
@@ -3066,6 +3127,23 @@ static void move_task(struct task_struct *p, struct lb_env *env)
check_preempt_curr(env->dst_rq, p, 0);
}

+static int task_numa_hot(struct task_struct *p, int from_cpu, int to_cpu)
+{
+ int from_dist, to_dist;
+ int node = tsk_home_node(p);
+
+ if (!sched_feat_numa(NUMA_HOT) || node == -1)
+ return 0; /* no node preference */
+
+ from_dist = node_distance(cpu_to_node(from_cpu), node);
+ to_dist = node_distance(cpu_to_node(to_cpu), node);
+
+ if (to_dist < from_dist)
+ return 0; /* getting closer is ok */
+
+ return 1; /* stick to where we are */
+}
+
/*
* Is this task likely cache-hot:
*/
@@ -3151,6 +3229,7 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
*/

tsk_cache_hot = task_hot(p, env->src_rq->clock_task, env->sd);
+ tsk_cache_hot |= task_numa_hot(p, env->src_cpu, env->dst_cpu);
if (!tsk_cache_hot ||
env->sd->nr_balance_failed > env->sd->cache_nice_tries) {
#ifdef CONFIG_SCHEDSTATS
@@ -3176,11 +3255,11 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
*
* Called with both runqueues locked.
*/
-static int move_one_task(struct lb_env *env)
+static int __move_one_task(struct lb_env *env)
{
struct task_struct *p, *n;

- list_for_each_entry_safe(p, n, &env->src_rq->cfs_tasks, se.group_node) {
+ list_for_each_entry_safe(p, n, env->tasks, se.group_node) {
if (throttled_lb_pair(task_group(p), env->src_rq->cpu, env->dst_cpu))
continue;

@@ -3199,6 +3278,21 @@ static int move_one_task(struct lb_env *env)
return 0;
}

+static int move_one_task(struct lb_env *env)
+{
+ if (sched_feat_numa(NUMA_PULL)) {
+ env->tasks = offnode_tasks(env->src_rq);
+ if (__move_one_task(env))
+ return 1;
+ }
+
+ env->tasks = &env->src_rq->cfs_tasks;
+ if (__move_one_task(env))
+ return 1;
+
+ return 0;
+}
+
static unsigned long task_h_load(struct task_struct *p);

static const unsigned int sched_nr_migrate_break = 32;
@@ -3212,7 +3306,6 @@ static const unsigned int sched_nr_migrate_break = 32;
*/
static int move_tasks(struct lb_env *env)
{
- struct list_head *tasks = &env->src_rq->cfs_tasks;
struct task_struct *p;
unsigned long load;
int pulled = 0;
@@ -3220,8 +3313,9 @@ static int move_tasks(struct lb_env *env)
if (env->imbalance <= 0)
return 0;

- while (!list_empty(tasks)) {
- p = list_first_entry(tasks, struct task_struct, se.group_node);
+again:
+ while (!list_empty(env->tasks)) {
+ p = list_first_entry(env->tasks, struct task_struct, se.group_node);

env->loop++;
/* We've more or less seen every task there is, call it quits */
@@ -3232,7 +3326,7 @@ static int move_tasks(struct lb_env *env)
if (env->loop > env->loop_break) {
env->loop_break += sched_nr_migrate_break;
env->flags |= LBF_NEED_BREAK;
- break;
+ goto out;
}

if (throttled_lb_pair(task_group(p), env->src_cpu, env->dst_cpu))
@@ -3260,7 +3354,7 @@ static int move_tasks(struct lb_env *env)
* the critical section.
*/
if (env->idle == CPU_NEWLY_IDLE)
- break;
+ goto out;
#endif

/*
@@ -3268,13 +3362,20 @@ static int move_tasks(struct lb_env *env)
* weighted load.
*/
if (env->imbalance <= 0)
- break;
+ goto out;

continue;
next:
- list_move_tail(&p->se.group_node, tasks);
+ list_move_tail(&p->se.group_node, env->tasks);
+ }
+
+ if (env->tasks == offnode_tasks(env->src_rq)) {
+ env->tasks = &env->src_rq->cfs_tasks;
+ env->loop = 0;
+ goto again;
}

+out:
/*
* Right now, this is one of only two places move_task() is called,
* so we can safely collect move_task() stats here rather than
@@ -3429,6 +3530,11 @@ struct sd_lb_stats {
unsigned int busiest_group_weight;

int group_imb; /* Is there imbalance in this sd */
+#ifdef CONFIG_SCHED_NUMA
+ struct sched_group *numa_group; /* group which has offnode_tasks */
+ unsigned long numa_group_weight;
+ unsigned long numa_group_running;
+#endif
};

/*
@@ -3444,6 +3550,10 @@ struct sg_lb_stats {
unsigned long 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_SCHED_NUMA
+ unsigned long numa_weight;
+ unsigned long numa_running;
+#endif
};

/**
@@ -3472,6 +3582,110 @@ static inline int get_sd_load_idx(struct sched_domain *sd,
return load_idx;
}

+#ifdef CONFIG_SCHED_NUMA
+static inline void update_sg_numa_stats(struct sg_lb_stats *sgs, struct rq *rq)
+{
+ sgs->numa_weight += rq->offnode_weight;
+ sgs->numa_running += rq->offnode_running;
+}
+
+/*
+ * Since the offnode lists are indiscriminate (they contain tasks for all other
+ * nodes) it is impossible to say if there's any task on there that wants to
+ * move towards the pulling cpu. Therefore select a random offnode list to pull
+ * from such that eventually we'll try them all.
+ *
+ * Select a random group that has offnode tasks as sds->numa_group
+ */
+static inline void update_sd_numa_stats(struct sched_domain *sd,
+ struct sched_group *group, struct sd_lb_stats *sds,
+ int local_group, struct sg_lb_stats *sgs)
+{
+ if (!(sd->flags & SD_NUMA))
+ return;
+
+ if (local_group)
+ return;
+
+ if (!sgs->numa_running)
+ return;
+
+ if (!sds->numa_group || pick_numa_rand(sd->span_weight / group->group_weight)) {
+ sds->numa_group = group;
+ sds->numa_group_weight = sgs->numa_weight;
+ sds->numa_group_running = sgs->numa_running;
+ }
+}
+
+/*
+ * Pick a random queue from the group that has offnode tasks.
+ */
+static struct rq *find_busiest_numa_queue(struct lb_env *env,
+ struct sched_group *group)
+{
+ struct rq *busiest = NULL, *rq;
+ int cpu;
+
+ for_each_cpu_and(cpu, sched_group_cpus(group), env->cpus) {
+ rq = cpu_rq(cpu);
+ if (!rq->offnode_running)
+ continue;
+ if (!busiest || pick_numa_rand(group->group_weight))
+ busiest = rq;
+ }
+
+ return busiest;
+}
+
+/*
+ * Called in case of no other imbalance, if there is a queue running offnode
+ * tasksk we'll say we're imbalanced anyway to nudge these tasks towards their
+ * proper node.
+ */
+static inline int check_numa_busiest_group(struct lb_env *env, struct sd_lb_stats *sds)
+{
+ if (!sched_feat(NUMA_PULL_BIAS))
+ return 0;
+
+ if (!sds->numa_group)
+ return 0;
+
+ env->imbalance = sds->numa_group_weight / sds->numa_group_running;
+ sds->busiest = sds->numa_group;
+ env->find_busiest_queue = find_busiest_numa_queue;
+ return 1;
+}
+
+static inline bool need_active_numa_balance(struct lb_env *env)
+{
+ return env->find_busiest_queue == find_busiest_numa_queue &&
+ env->src_rq->offnode_running == 1 &&
+ env->src_rq->nr_running == 1;
+}
+
+#else /* CONFIG_SCHED_NUMA */
+
+static inline void update_sg_numa_stats(struct sg_lb_stats *sgs, struct rq *rq)
+{
+}
+
+static inline void update_sd_numa_stats(struct sched_domain *sd,
+ struct sched_group *group, struct sd_lb_stats *sds,
+ int local_group, struct sg_lb_stats *sgs)
+{
+}
+
+static inline int check_numa_busiest_group(struct lb_env *env, struct sd_lb_stats *sds)
+{
+ return 0;
+}
+
+static inline bool need_active_numa_balance(struct lb_env *env)
+{
+ return false;
+}
+#endif /* CONFIG_SCHED_NUMA */
+
unsigned long default_scale_freq_power(struct sched_domain *sd, int cpu)
{
return SCHED_POWER_SCALE;
@@ -3687,6 +3901,8 @@ static inline void update_sg_lb_stats(struct lb_env *env,
sgs->sum_weighted_load += weighted_cpuload(i);
if (idle_cpu(i))
sgs->idle_cpus++;
+
+ update_sg_numa_stats(sgs, rq);
}

/*
@@ -3840,6 +4056,8 @@ static inline void update_sd_lb_stats(struct lb_env *env,
sds->group_imb = sgs.group_imb;
}

+ update_sd_numa_stats(env->sd, sg, sds, local_group, &sgs);
+
sg = sg->next;
} while (sg != env->sd->groups);
}
@@ -4126,6 +4344,9 @@ force_balance:
return sds.busiest;

out_balanced:
+ if (check_numa_busiest_group(env, &sds))
+ return sds.busiest;
+
ret:
env->imbalance = 0;
return NULL;
@@ -4204,6 +4425,9 @@ static int need_active_balance(struct lb_env *env)
return 1;
}

+ if (need_active_numa_balance(env))
+ return 1;
+
return unlikely(sd->nr_balance_failed > sd->cache_nice_tries+2);
}

@@ -4256,6 +4480,8 @@ redo:
schedstat_inc(sd, lb_nobusyq[idle]);
goto out_balanced;
}
+ env.src_rq = busiest;
+ env.src_cpu = busiest->cpu;

BUG_ON(busiest == env.dst_rq);

@@ -4274,6 +4500,10 @@ redo:
env.src_cpu = busiest->cpu;
env.src_rq = busiest;
env.loop_max = min(sysctl_sched_nr_migrate, busiest->nr_running);
+ if (sched_feat_numa(NUMA_PULL))
+ env.tasks = offnode_tasks(busiest);
+ else
+ env.tasks = &busiest->cfs_tasks;

update_h_load(env.src_cpu);
more_balance:
diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index eebefca..a5cc07b 100644
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -61,3 +61,11 @@ SCHED_FEAT(TTWU_QUEUE, true)
SCHED_FEAT(FORCE_SD_OVERLAP, false)
SCHED_FEAT(RT_RUNTIME_SHARE, true)
SCHED_FEAT(LB_MIN, false)
+
+#ifdef CONFIG_SCHED_NUMA
+SCHED_FEAT(NUMA_HOT, true)
+SCHED_FEAT(NUMA_BIAS, true)
+SCHED_FEAT(NUMA_PULL, true)
+SCHED_FEAT(NUMA_PULL_BIAS, true)
+#endif
+
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 741272e..74c37e6 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -418,6 +418,12 @@ struct rq {

struct list_head cfs_tasks;

+#ifdef CONFIG_SCHED_NUMA
+ unsigned long offnode_running;
+ unsigned long offnode_weight;
+ struct list_head offnode_tasks;
+#endif
+
u64 rt_avg;
u64 age_stamp;
u64 idle_stamp;
@@ -469,6 +475,15 @@ struct rq {
#endif
};

+static inline struct list_head *offnode_tasks(struct rq *rq)
+{
+#ifdef CONFIG_SCHED_NUMA
+ return &rq->offnode_tasks;
+#else
+ return NULL;
+#endif
+}
+
static inline int cpu_of(struct rq *rq)
{
#ifdef CONFIG_SMP
@@ -529,6 +544,7 @@ static inline struct sched_domain *highest_flag_domain(int cpu, int flag)

DECLARE_PER_CPU(struct sched_domain *, sd_llc);
DECLARE_PER_CPU(int, sd_llc_id);
+DECLARE_PER_CPU(struct sched_domain *, sd_node);

extern int group_balance_cpu(struct sched_group *sg);

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