sched/numa: Reschedule task on preferred NUMA node once selected
A preferred node is selected based on the node the most NUMA hinting
faults was incurred on. There is no guarantee that the task is running
on that node at the time so this patch rescheules the task to run on
the most idle CPU of the selected node when selected. This avoids
waiting for the balancer to make a decision.
Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1381141781-10992-25-git-send-email-mgorman@suse.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8943124..8b15e9e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -886,6 +886,31 @@
*/
unsigned int sysctl_numa_balancing_settle_count __read_mostly = 3;
+static unsigned long weighted_cpuload(const int cpu);
+
+
+static int
+find_idlest_cpu_node(int this_cpu, int nid)
+{
+ unsigned long load, min_load = ULONG_MAX;
+ int i, idlest_cpu = this_cpu;
+
+ BUG_ON(cpu_to_node(this_cpu) == nid);
+
+ rcu_read_lock();
+ for_each_cpu(i, cpumask_of_node(nid)) {
+ load = weighted_cpuload(i);
+
+ if (load < min_load) {
+ min_load = load;
+ idlest_cpu = i;
+ }
+ }
+ rcu_read_unlock();
+
+ return idlest_cpu;
+}
+
static void task_numa_placement(struct task_struct *p)
{
int seq, nid, max_nid = -1;
@@ -916,10 +941,29 @@
}
}
- /* Update the tasks preferred node if necessary */
+ /*
+ * Record the preferred node as the node with the most faults,
+ * requeue the task to be running on the idlest CPU on the
+ * preferred node and reset the scanning rate to recheck
+ * the working set placement.
+ */
if (max_faults && max_nid != p->numa_preferred_nid) {
+ int preferred_cpu;
+
+ /*
+ * If the task is not on the preferred node then find the most
+ * idle CPU to migrate to.
+ */
+ preferred_cpu = task_cpu(p);
+ if (cpu_to_node(preferred_cpu) != max_nid) {
+ preferred_cpu = find_idlest_cpu_node(preferred_cpu,
+ max_nid);
+ }
+
+ /* Update the preferred nid and migrate task if possible */
p->numa_preferred_nid = max_nid;
p->numa_migrate_seq = 0;
+ migrate_task_to(p, preferred_cpu);
}
}
