[PATCH] powerpc: VPHN topology change updates all siblings

[PATCH] powerpc: VPHN topology change updates all siblings

[Robert Jennings]

When an associativity level change is found for one thread, the
siblings threads need to be updated as well.  This is done today
for PRRN in stage_topology_update() but is missing for VPHN in
update_cpu_associativity_changes_mask().

All threads should be updated to move to the new node.  Without this
patch, a single thread may be flagged for a topology change, leaving it
in a different node from its siblings, which is incorrect.  This causes
problems for the scheduler where overlapping scheduler groups are created
and a loop is formed in those groups.

Reported-by: Jan Stancek <jstancek@redhat.com>
Signed-off-by: Robert Jennings <rcj@linux.vnet.ibm.com>
Cc: <stable@vger.kernel.org>
---
Looking to get this fix in 3.11.
This is requested for the 3.10 stable tree as well, it fixes a
bug that presents as a scheduler issue when VPHN is active.
VPHN was enabled in the v3.9 window in commit b7abef0.
---
 arch/powerpc/mm/numa.c | 59
 +++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 44 insertions(+), 15 deletions(-)

diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index 0839721..5850798 100644
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c
@@ -27,6 +27,7 @@
 #include <linux/seq_file.h>
 #include <linux/uaccess.h>
 #include <linux/slab.h>
+#include <asm/cputhreads.h>
 #include <asm/sparsemem.h>
 #include <asm/prom.h>
 #include <asm/smp.h>
@@ -1318,7 +1319,8 @@ static int update_cpu_associativity_changes_mask(void)
 			}
 		}
 		if (changed) {
-			cpumask_set_cpu(cpu, changes);
+			cpumask_or(changes, changes, cpu_sibling_mask(cpu));
+			cpu = cpu_last_thread_sibling(cpu);
 		}
 	}
 
@@ -1426,7 +1428,7 @@ static int update_cpu_topology(void *data)
 	if (!data)
 		return -EINVAL;
 
-	cpu = get_cpu();
+	cpu = smp_processor_id();
 
 	for (update = data; update; update = update->next) {
 		if (cpu != update->cpu)
@@ -1446,12 +1448,12 @@ static int update_cpu_topology(void *data)
  */
 int arch_update_cpu_topology(void)
 {
-	unsigned int cpu, changed = 0;
+	unsigned int cpu, sibling, changed = 0;
 	struct topology_update_data *updates, *ud;
 	unsigned int associativity[VPHN_ASSOC_BUFSIZE] = {0};
 	cpumask_t updated_cpus;
 	struct device *dev;
-	int weight, i = 0;
+	int weight, new_nid, i = 0;
 
 	weight = cpumask_weight(&cpu_associativity_changes_mask);
 	if (!weight)
@@ -1464,19 +1466,46 @@ int arch_update_cpu_topology(void)
 	cpumask_clear(&updated_cpus);
 
 	for_each_cpu(cpu, &cpu_associativity_changes_mask) {
-		ud = &updates[i++];
-		ud->cpu = cpu;
-		vphn_get_associativity(cpu, associativity);
-		ud->new_nid = associativity_to_nid(associativity);
-
-		if (ud->new_nid < 0 || !node_online(ud->new_nid))
-			ud->new_nid = first_online_node;
+		/*
+		 * If siblings aren't flagged for changes, updates list
+		 * will be too short. Skip on this update and set for next
+		 * update.
+		 */
+		if (!cpumask_subset(cpu_sibling_mask(cpu),
+					&cpu_associativity_changes_mask)) {
+			pr_info("Sibling bits not set for associativity "
+					"change, cpu%d\n", cpu);
+			cpumask_or(&cpu_associativity_changes_mask,
+					&cpu_associativity_changes_mask,
+					cpu_sibling_mask(cpu));
+			cpu = cpu_last_thread_sibling(cpu);
+			continue;
+		}
 
-		ud->old_nid = numa_cpu_lookup_table[cpu];
-		cpumask_set_cpu(cpu, &updated_cpus);
+		/* Use associativity from first thread for all siblings */
+		vphn_get_associativity(cpu, associativity);
+		new_nid = associativity_to_nid(associativity);
+		if (new_nid < 0 || !node_online(new_nid))
+			new_nid = first_online_node;
+
+		if (new_nid == numa_cpu_lookup_table[cpu]) {
+			cpumask_andnot(&cpu_associativity_changes_mask,
+					&cpu_associativity_changes_mask,
+					cpu_sibling_mask(cpu));
+			cpu = cpu_last_thread_sibling(cpu);
+			continue;
+		}
 
-		if (i < weight)
-			ud->next = &updates[i];
+		for_each_cpu(sibling, cpu_sibling_mask(cpu)) {
+			ud = &updates[i++];
+			ud->cpu = sibling;
+			ud->new_nid = new_nid;
+			ud->old_nid = numa_cpu_lookup_table[sibling];
+			cpumask_set_cpu(sibling, &updated_cpus);
+			if (i < weight)
+				ud->next = &updates[i];
+		}
+		cpu = cpu_last_thread_sibling(cpu);
 	}
 
 	stop_machine(update_cpu_topology, &updates[0], &updated_cpus);
-- 
1.8.1.2

Re: [PATCH] powerpc: VPHN topology change updates all siblings

[Benjamin Herrenschmidt]

On Tue, 2013-07-23 at 07:33 -0500, Robert Jennings wrote:
> When an associativity level change is found for one thread, the
> siblings threads need to be updated as well.  This is done today
> for PRRN in stage_topology_update() but is missing for VPHN in
> update_cpu_associativity_changes_mask().
> 
> All threads should be updated to move to the new node.  Without this
> patch, a single thread may be flagged for a topology change, leaving it
> in a different node from its siblings, which is incorrect.  This causes
> problems for the scheduler where overlapping scheduler groups are created
> and a loop is formed in those groups.
> 
> Reported-by: Jan Stancek <jstancek@redhat.com>
> Signed-off-by: Robert Jennings <rcj@linux.vnet.ibm.com>
> Cc: <stable@vger.kernel.org>

Patch breaks the UP build ...

Cheers,
Ben.

Re: [PATCH] powerpc: VPHN topology change updates all siblings

[Robert Jennings]

* Benjamin Herrenschmidt (benh@kernel.crashing.org) wrote:
> On Tue, 2013-07-23 at 07:33 -0500, Robert Jennings wrote:
> > When an associativity level change is found for one thread, the
> > siblings threads need to be updated as well.  This is done today
> > for PRRN in stage_topology_update() but is missing for VPHN in
> > update_cpu_associativity_changes_mask().
> > 
> > All threads should be updated to move to the new node.  Without this
> > patch, a single thread may be flagged for a topology change, leaving it
> > in a different node from its siblings, which is incorrect.  This causes
> > problems for the scheduler where overlapping scheduler groups are created
> > and a loop is formed in those groups.
> > 
> > Reported-by: Jan Stancek <jstancek@redhat.com>
> > Signed-off-by: Robert Jennings <rcj@linux.vnet.ibm.com>
> > Cc: <stable@vger.kernel.org>
> 
> Patch breaks the UP build ...
> 
> Cheers,
> Ben.

Very sorry about that, a fix is on the way.