sched/numa: Update NUMA hinting faults once per scan
NUMA hinting fault counts and placement decisions are both recorded in the
same array which distorts the samples in an unpredictable fashion. The values
linearly accumulate during the scan and then decay creating a sawtooth-like
pattern in the per-node counts. It also means that placement decisions are
time sensitive. At best it means that it is very difficult to state that
the buffer holds a decaying average of past faulting behaviour. At worst,
it can confuse the load balancer if it sees one node with an artifically high
count due to very recent faulting activity and may create a bouncing effect.
This patch adds a second array. numa_faults stores the historical data
which is used for placement decisions. numa_faults_buffer holds the
fault activity during the current scan window. When the scan completes,
numa_faults decays and the values from numa_faults_buffer are copied
across.
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/1381141781-10992-22-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 9efd34f..3abc651 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -892,8 +892,14 @@
/* Find the node with the highest number of faults */
for_each_online_node(nid) {
- unsigned long faults = p->numa_faults[nid];
+ unsigned long faults;
+
+ /* Decay existing window and copy faults since last scan */
p->numa_faults[nid] >>= 1;
+ p->numa_faults[nid] += p->numa_faults_buffer[nid];
+ p->numa_faults_buffer[nid] = 0;
+
+ faults = p->numa_faults[nid];
if (faults > max_faults) {
max_faults = faults;
max_nid = nid;
@@ -919,9 +925,13 @@
if (unlikely(!p->numa_faults)) {
int size = sizeof(*p->numa_faults) * nr_node_ids;
- p->numa_faults = kzalloc(size, GFP_KERNEL|__GFP_NOWARN);
+ /* numa_faults and numa_faults_buffer share the allocation */
+ p->numa_faults = kzalloc(size * 2, GFP_KERNEL|__GFP_NOWARN);
if (!p->numa_faults)
return;
+
+ BUG_ON(p->numa_faults_buffer);
+ p->numa_faults_buffer = p->numa_faults + nr_node_ids;
}
/*
@@ -939,7 +949,7 @@
task_numa_placement(p);
- p->numa_faults[node] += pages;
+ p->numa_faults_buffer[node] += pages;
}
static void reset_ptenuma_scan(struct task_struct *p)