[ovs-dev] [emc processing optimization v2 (rebase) 1/2] dpif-netdev: Load packet pointer only once in emc_processing()

[Andy Zhou]

For the machines I have access to, Reloading the same pointer from
memory seems to inhibit complier optimization somewhat.

In emc_processing(), using a single packet pointer, instead reloading
it from memory with packets[i], improves performance by 0.3 Mpps (tested
with 10G NIC pushing 64 byte packets, with the base line of 12.2 Mpps).

Besides improving performance, this patch should also improves code
readability.

Signed-off-by: Andy Zhou <azhou at ovn.org>
---
 lib/dpif-netdev.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
index 9abb948..c619b86 100644
--- a/lib/dpif-netdev.c
+++ b/lib/dpif-netdev.c
@@ -3301,9 +3301,10 @@ emc_processing(struct dp_netdev_pmd_thread *pmd, struct dp_packet **packets,
 
     for (i = 0; i < cnt; i++) {
         struct dp_netdev_flow *flow;
+        struct dp_packet *packet = packets[i];
 
-        if (OVS_UNLIKELY(dp_packet_size(packets[i]) < ETH_HEADER_LEN)) {
-            dp_packet_delete(packets[i]);
+        if (OVS_UNLIKELY(dp_packet_size(packet) < ETH_HEADER_LEN)) {
+            dp_packet_delete(packet);
             n_dropped++;
             continue;
         }
@@ -3316,16 +3317,16 @@ emc_processing(struct dp_netdev_pmd_thread *pmd, struct dp_packet **packets,
         struct netdev_flow_key *key = &keys[n_missed];
         miniflow_extract(packets[i], &key->mf);
         key->len = 0; /* Not computed yet. */
-        key->hash = dpif_netdev_packet_get_rss_hash(packets[i], &key->mf);
+        key->hash = dpif_netdev_packet_get_rss_hash(packet, &key->mf);
 
         flow = emc_lookup(flow_cache, key);
         if (OVS_LIKELY(flow)) {
-            dp_netdev_queue_batches(packets[i], flow, &key->mf, batches,
+            dp_netdev_queue_batches(packet, flow, &key->mf, batches,
                                     n_batches);
         } else {
             /* Exact match cache missed. Group missed packets together at
              * the beginning of the 'packets' array.  */
-            packets[n_missed++] = packets[i];
+            packets[n_missed++] = packet;
         }
     }
 
-- 
1.9.1