Xen devel - Sep 2013 - [PATCH] xen: numa-sched: leave node-affinity alone if not in "auto" mode

If the domain''s NUMA node-affinity is being specified by the
user/toolstack (instead of being automatically computed by Xen),
we really should stick to that. This means domain_update_node_affinity()
is wrong when it filters out some stuff from there even in "!auto"
mode.

This commit fixes that. Of course, this does not mean node-affinity
is always honoured (e.g., a vcpu won''t run on a pcpu of a different
cpupool) but the necessary logic for taking into account all the
possible situations lives in the scheduler code, where it belongs.

What could happen without this change is that, under certain
circumstances, the node-affinity of a domain may change when the
user modifies the vcpu-affinity of the domain''s vcpus. This, even
if probably not a real bug, is at least something the user does
not expect, so let''s avoid it.

Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
Cc: George Dunlap <George.Dunlap@eu.citrix.com>
Cc: Keir Fraser <keir@xen.org>
---
 xen/common/domain.c |   28 +++++++++-------------------
 1 file changed, 9 insertions(+), 19 deletions(-)

diff --git a/xen/common/domain.c b/xen/common/domain.c
index 5999779..af31ab4 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -352,7 +352,6 @@ void domain_update_node_affinity(struct domain *d)
     cpumask_var_t cpumask;
     cpumask_var_t online_affinity;
     const cpumask_t *online;
-    nodemask_t nodemask = NODE_MASK_NONE;
     struct vcpu *v;
     unsigned int node;
 
@@ -374,28 +373,19 @@ void domain_update_node_affinity(struct domain *d)
         cpumask_or(cpumask, cpumask, online_affinity);
     }
 
+    /*
+     * If d->auto_node_affinity is true, the domain''s node-affinity
mask
+     * (d->node_affinity) is automaically computed from all the
domain''s
+     * vcpus'' vcpu-affinity masks (the union of which we have just
built
+     * above in cpumask). OTOH, if d->auto_node_affinity is false, we
+     * must leave the node-affinity of the domain alone.
+     */
     if ( d->auto_node_affinity )
     {
-        /* Node-affinity is automaically computed from all vcpu-affinities */
+        nodes_clear(d->node_affinity);
         for_each_online_node ( node )
             if ( cpumask_intersects(&node_to_cpumask(node), cpumask) )
-                node_set(node, nodemask);
-
-        d->node_affinity = nodemask;
-    }
-    else
-    {
-        /* Node-affinity is provided by someone else, just filter out cpus
-         * that are either offline or not in the affinity of any vcpus. */
-        nodemask = d->node_affinity;
-        for_each_node_mask ( node, d->node_affinity )
-            if ( !cpumask_intersects(&node_to_cpumask(node), cpumask) )
-                node_clear(node, nodemask);//d->node_affinity);
-
-        /* Avoid loosing track of node-affinity because of a bad
-         * vcpu-affinity has been specified. */
-        if ( !nodes_empty(nodemask) )
-            d->node_affinity = nodemask;
+                node_set(node, d->node_affinity);
     }
 
     sched_set_node_affinity(d, &d->node_affinity);

On 18/09/13 00:17, Dario Faggioli wrote:
> If the domain''s NUMA node-affinity is being specified by the
> user/toolstack (instead of being automatically computed by Xen),
> we really should stick to that. This means domain_update_node_affinity()
> is wrong when it filters out some stuff from there even in
"!auto"
> mode.
>
> This commit fixes that. Of course, this does not mean node-affinity
> is always honoured (e.g., a vcpu won''t run on a pcpu of a
different
> cpupool) but the necessary logic for taking into account all the
> possible situations lives in the scheduler code, where it belongs.
>
> What could happen without this change is that, under certain
> circumstances, the node-affinity of a domain may change when the
> user modifies the vcpu-affinity of the domain''s vcpus. This, even
> if probably not a real bug, is at least something the user does
> not expect, so let''s avoid it.
>
> Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
Reviewed-by: George Dunlap <george.dunlap@eu.citrix.com>