datapath: simplify ovs_flow_tbl_lookup_stats()

Simplify flow mask cache replacement without using expensive atomic
memory access to the mask pointers.

Signed-off-by: Andy Zhou <azhou@nicira.com>
Acked-by: Pravin B Shelar <pshelar@nicira.com>

diff --git a/datapath/flow_table.c b/datapath/flow_table.c
index 58a25c7..a18c095 100644 (file)
--- a/datapath/flow_table.c
+++ b/datapath/flow_table.c
@@ -554,7 +554,7 @@ struct sw_flow *ovs_flow_tbl_lookup_stats(struct flow_table *tbl,
 {
        struct mask_array *ma = rcu_dereference_ovsl(tbl->mask_array);
        struct table_instance *ti = rcu_dereference_ovsl(tbl->ti);
-       struct mask_cache_entry  *entries, *ce, *del;
+       struct mask_cache_entry *entries, *ce;
        struct sw_flow *flow;
        u32 hash = skb_hash;
        int seg;
@@ -566,42 +566,40 @@ struct sw_flow *ovs_flow_tbl_lookup_stats(struct flow_table *tbl,
                return flow_lookup(tbl, ti, ma, key, n_mask_hit, &mask_index);
        }
 
-       del = NULL;
+       ce = NULL;
        entries = this_cpu_ptr(tbl->mask_cache);
 
+       /* Find the cache entry 'ce' to operate on. */
        for (seg = 0; seg < MC_HASH_SEGS; seg++) {
-               int index;
+               int index = hash & (MC_HASH_ENTRIES - 1);
+               struct mask_cache_entry *e;
 
-               index = hash & (MC_HASH_ENTRIES - 1);
-               ce = &entries[index];
+               e = &entries[index];
+               if (e->skb_hash == skb_hash) {
+                       struct sw_flow_mask *cache;
 
-               if (ce->skb_hash == skb_hash) {
-                       struct sw_flow_mask *mask;
-
-                       mask = rcu_dereference_ovsl(ma->masks[ce->mask_index]);
-                       if (mask) {
-                               flow = masked_flow_lookup(ti, key, mask,
+                       cache = rcu_dereference_ovsl(ma->masks[e->mask_index]);
+                       if (cache) {
+                               flow = masked_flow_lookup(ti, key, cache,
                                                          n_mask_hit);
-                               if (flow)  /* Found */
+                               if (flow) /* Cache hit. */
                                        return flow;
-
                        }
-                       del = ce;
+                       e->skb_hash = 0;
+                       ce = e;  /* The best cache replacement candidate. */
                        break;
                }
 
-               if (!del || (del->skb_hash && !ce->skb_hash) ||
-                   (rcu_dereference_ovsl(ma->masks[del->mask_index]) &&
-                   !rcu_dereference_ovsl(ma->masks[ce->mask_index]))) {
-                       del = ce;
-               }
+               if (!ce || e->skb_hash < ce->skb_hash)
+                       ce = e;  /* A better replacement cache candidate. */
 
                hash >>= MC_HASH_SHIFT;
        }
 
-       flow = flow_lookup(tbl, ti, ma, key, n_mask_hit, &del->mask_index);
+       /* Cache miss, do full lookup. */
+       flow = flow_lookup(tbl, ti, ma, key, n_mask_hit, &ce->mask_index);
        if (flow)
-               del->skb_hash = skb_hash;
+               ce->skb_hash = skb_hash;
 
        return flow;
 }