[PATCH 1/2] powerpc/numa: improve control of topology updates

[Nathan Lynch]

When booted with "topology_updates=no", or when "off" is written to
/proc/powerpc/topology_updates, NUMA reassignments are inhibited for
PRRN and VPHN events. However, migration and suspend unconditionally
re-enable reassignments via start_topology_update(). This is
incoherent.

Check the topology_updates_enabled flag in
start/stop_topology_update() so that callers of those APIs need not be
aware of whether reassignments are enabled. This allows the
administrative decision on reassignments to remain in force across
migrations and suspensions.

Signed-off-by: Nathan Lynch <nathanl at linux.ibm.com>
---
 arch/powerpc/mm/numa.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index f976676004ad..48c9a97eb2c3 100644
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c
@@ -1498,6 +1498,9 @@ int start_topology_update(void)
 {
 	int rc = 0;
 
+	if (!topology_updates_enabled)
+		return 0;
+
 	if (firmware_has_feature(FW_FEATURE_PRRN)) {
 		if (!prrn_enabled) {
 			prrn_enabled = 1;
@@ -1531,6 +1534,9 @@ int stop_topology_update(void)
 {
 	int rc = 0;
 
+	if (!topology_updates_enabled)
+		return 0;
+
 	if (prrn_enabled) {
 		prrn_enabled = 0;
 #ifdef CONFIG_SMP
@@ -1588,11 +1594,13 @@ static ssize_t topology_write(struct file *file, const char __user *buf,
 
 	kbuf[read_len] = '\0';
 
-	if (!strncmp(kbuf, "on", 2))
+	if (!strncmp(kbuf, "on", 2)) {
+		topology_updates_enabled = true;
 		start_topology_update();
-	else if (!strncmp(kbuf, "off", 3))
+	} else if (!strncmp(kbuf, "off", 3)) {
 		stop_topology_update();
-	else
+		topology_updates_enabled = false;
+	} else
 		return -EINVAL;
 
 	return count;
@@ -1607,9 +1615,7 @@ static const struct file_operations topology_ops = {
 
 static int topology_update_init(void)
 {
-	/* Do not poll for changes if disabled at boot */
-	if (topology_updates_enabled)
-		start_topology_update();
+	start_topology_update();
 
 	if (vphn_enabled)
 		topology_schedule_update();
-- 
2.20.1