[tip:sched/numa] sched/numa: Build per numa_group active node mask from numa_faults_cpu statistics

From: tip-bot for Rik van Riel
Date: Tue Jan 28 2014 - 14:24:46 EST


Commit-ID: 20e07dea286a90f096a779706861472d296397c6
Gitweb: http://git.kernel.org/tip/20e07dea286a90f096a779706861472d296397c6
Author: Rik van Riel <riel@xxxxxxxxxx>
AuthorDate: Mon, 27 Jan 2014 17:03:43 -0500
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 28 Jan 2014 13:17:06 +0100

sched/numa: Build per numa_group active node mask from numa_faults_cpu statistics

The numa_faults_cpu statistics are used to maintain an active_nodes nodemask
per numa_group. This allows us to be smarter about when to do numa migrations.

Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Chegu Vinod <chegu_vinod@xxxxxx>
Link: http://lkml.kernel.org/r/1390860228-21539-5-git-send-email-riel@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/sched/fair.c | 42 ++++++++++++++++++++++++++++++++++++++++++
1 file changed, 42 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 4841aaf..1ee921f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -885,6 +885,7 @@ struct numa_group {
struct list_head task_list;

struct rcu_head rcu;
+ nodemask_t active_nodes;
unsigned long total_faults;
unsigned long *faults_cpu;
unsigned long faults[0];
@@ -918,6 +919,12 @@ static inline unsigned long group_faults(struct task_struct *p, int nid)
p->numa_group->faults[task_faults_idx(nid, 1)];
}

+static inline unsigned long group_faults_cpu(struct numa_group *group, int nid)
+{
+ return group->faults_cpu[task_faults_idx(nid, 0)] +
+ group->faults_cpu[task_faults_idx(nid, 1)];
+}
+
/*
* These return the fraction of accesses done by a particular task, or
* task group, on a particular numa node. The group weight is given a
@@ -1271,6 +1278,38 @@ static void numa_migrate_preferred(struct task_struct *p)
}

/*
+ * Find the nodes on which the workload is actively running. We do this by
+ * tracking the nodes from which NUMA hinting faults are triggered. This can
+ * be different from the set of nodes where the workload's memory is currently
+ * located.
+ *
+ * The bitmask is used to make smarter decisions on when to do NUMA page
+ * migrations, To prevent flip-flopping, and excessive page migrations, nodes
+ * are added when they cause over 6/16 of the maximum number of faults, but
+ * only removed when they drop below 3/16.
+ */
+static void update_numa_active_node_mask(struct numa_group *numa_group)
+{
+ unsigned long faults, max_faults = 0;
+ int nid;
+
+ for_each_online_node(nid) {
+ faults = group_faults_cpu(numa_group, nid);
+ if (faults > max_faults)
+ max_faults = faults;
+ }
+
+ for_each_online_node(nid) {
+ faults = group_faults_cpu(numa_group, nid);
+ if (!node_isset(nid, numa_group->active_nodes)) {
+ if (faults > max_faults * 6 / 16)
+ node_set(nid, numa_group->active_nodes);
+ } else if (faults < max_faults * 3 / 16)
+ node_clear(nid, numa_group->active_nodes);
+ }
+}
+
+/*
* When adapting the scan rate, the period is divided into NUMA_PERIOD_SLOTS
* increments. The more local the fault statistics are, the higher the scan
* period will be for the next scan window. If local/remote ratio is below
@@ -1412,6 +1451,7 @@ static void task_numa_placement(struct task_struct *p)
update_task_scan_period(p, fault_types[0], fault_types[1]);

if (p->numa_group) {
+ update_numa_active_node_mask(p->numa_group);
/*
* If the preferred task and group nids are different,
* iterate over the nodes again to find the best place.
@@ -1474,6 +1514,8 @@ static void task_numa_group(struct task_struct *p, int cpupid, int flags,
/* Second half of the array tracks nids where faults happen */
grp->faults_cpu = grp->faults + 2 * nr_node_ids;

+ node_set(task_node(current), grp->active_nodes);
+
for (i = 0; i < 4*nr_node_ids; i++)
grp->faults[i] = p->numa_faults_memory[i];

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