[ovs-dev] [PATCH] dpif-netdev: Optimize the exact match lookup.

[Tonghao Zhang]

When inserting or updating (e.g. emc_insert) a flow to EMC,
we compare (e.g the hash and miniflow ) the netdev_flow_key.
If the key is matched, we will update it. If we didn’t find
the miniflow in the cache, the new flow will be stored.

But when looking up the flow, we compare the hash and miniflow
of key and make sure it is alive. If a flow is not alive but
the key is matched, we still will go to next loop. More important,
we can’t find the flow in the next loop (the flow is not alive in
the previous loop). This patch simply compares the miniflows of
the packets.

The topo is shown as below. VM01 sends TCP packets to VM02, and
OvS forwards packtets.

        VM01 -- OVS+DPDK VM02 -- VM03

With this patch, the TCP throughput between VMs is
5.37, 5.45, 5.48, 5.59, 5.65, 5.60 Gbs/sec avg: 5.52 Gbs/sec

up to:
5.64, 5.65, 5.66, 5.67, 5.62, 5.67 Gbs/sec avg: 5.65 Gbs/sec

(maybe ~2.3% performance improve, but it is hard to tell exactly
due to variance in the test results).

Signed-off-by: Tonghao Zhang <xiangxia.m....@gmail.com>
---
 lib/dpif-netdev.c | 17 ++---------------
 1 file changed, 2 insertions(+), 15 deletions(-)

diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
index 47a9fa0..86a6073 100644
--- a/lib/dpif-netdev.c
+++ b/lib/dpif-netdev.c
@@ -1904,16 +1904,6 @@ netdev_flow_key_equal(const struct netdev_flow_key *a,
     return a->hash == b->hash && !memcmp(&a->mf, &b->mf, a->len);
 }
 
-/* Used to compare 'netdev_flow_key' in the exact match cache to a miniflow.
- * The maps are compared bitwise, so both 'key->mf' and 'mf' must have been
- * generated by miniflow_extract. */
-static inline bool
-netdev_flow_key_equal_mf(const struct netdev_flow_key *key,
-                         const struct miniflow *mf)
-{
-    return !memcmp(&key->mf, mf, key->len);
-}
-
 static inline void
 netdev_flow_key_clone(struct netdev_flow_key *dst,
                       const struct netdev_flow_key *src)
@@ -2088,12 +2078,9 @@ emc_lookup(struct emc_cache *cache, const struct 
netdev_flow_key *key)
     struct emc_entry *current_entry;
 
     EMC_FOR_EACH_POS_WITH_HASH(cache, current_entry, key->hash) {
-        if (current_entry->key.hash == key->hash
-            && emc_entry_alive(current_entry)
-            && netdev_flow_key_equal_mf(&current_entry->key, &key->mf)) {
-
+        if (netdev_flow_key_equal(&current_entry->key, key)) {
             /* We found the entry with the 'key->mf' miniflow */
-            return current_entry->flow;
+            return emc_entry_alive(current_entry) ? current_entry->flow : NULL;
         }
     }
 
-- 
1.8.3.1

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