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Subject[PATCH 3/8] sched: Select a preferred node with the most numa hinting faults
Date
This patch selects a preferred node for a task to run on based on the
NUMA hinting faults. This information is later used to migrate tasks
towards the node during balancing.

Signed-off-by: Mel Gorman <mgorman@suse.de>
---
include/linux/sched.h | 1 +
kernel/sched/core.c | 10 ++++++++++
kernel/sched/fair.c | 16 ++++++++++++++--
kernel/sched/sched.h | 2 +-
4 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 72861b4..ba46a64 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1507,6 +1507,7 @@ struct task_struct {
struct callback_head numa_work;

unsigned long *numa_faults;
+ int numa_preferred_nid;
#endif /* CONFIG_NUMA_BALANCING */

struct rcu_head rcu;
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f332ec0..019baae 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1593,6 +1593,7 @@ static void __sched_fork(struct task_struct *p)
p->numa_scan_seq = p->mm ? p->mm->numa_scan_seq : 0;
p->numa_migrate_seq = p->mm ? p->mm->numa_scan_seq - 1 : 0;
p->numa_scan_period = sysctl_numa_balancing_scan_delay;
+ p->numa_preferred_nid = -1;
p->numa_work.next = &p->numa_work;
p->numa_faults = NULL;
#endif /* CONFIG_NUMA_BALANCING */
@@ -5713,6 +5714,15 @@ enum s_alloc {

struct sched_domain_topology_level;

+#ifdef CONFIG_NUMA_BALANCING
+
+/* Set a tasks preferred NUMA node */
+void sched_setnuma(struct task_struct *p, int nid)
+{
+ p->numa_preferred_nid = nid;
+}
+#endif /* CONFIG_NUMA_BALANCING */
+
typedef struct sched_domain *(*sched_domain_init_f)(struct sched_domain_topology_level *tl, int cpu);
typedef const struct cpumask *(*sched_domain_mask_f)(int cpu);

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 904fd6f..f8c3f61 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -793,7 +793,8 @@ unsigned int sysctl_numa_balancing_scan_delay = 1000;

static void task_numa_placement(struct task_struct *p)
{
- int seq;
+ int seq, nid, max_nid = 0;
+ unsigned long max_faults = 0;

if (!p->mm) /* for example, ksmd faulting in a user's mm */
return;
@@ -802,7 +803,18 @@ static void task_numa_placement(struct task_struct *p)
return;
p->numa_scan_seq = seq;

- /* FIXME: Scheduling placement policy hints go here */
+ /* Find the node with the highest number of faults */
+ for (nid = 0; nid < nr_node_ids; nid++) {
+ unsigned long faults = p->numa_faults[nid];
+ p->numa_faults[nid] >>= 1;
+ if (faults > max_faults) {
+ max_faults = faults;
+ max_nid = nid;
+ }
+ }
+
+ if (max_faults && max_nid != p->numa_preferred_nid)
+ sched_setnuma(p, max_nid);
}

/*
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 9c26d88..65a0cf0 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -504,7 +504,7 @@ DECLARE_PER_CPU(struct rq, runqueues);
#define raw_rq() (&__raw_get_cpu_var(runqueues))

#ifdef CONFIG_NUMA_BALANCING
-extern void sched_setnuma(struct task_struct *p, int node, int shared);
+extern void sched_setnuma(struct task_struct *p, int nid);
static inline void task_numa_free(struct task_struct *p)
{
kfree(p->numa_faults);
--
1.8.1.4


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