dpif-netdev: Prefetch next packet before miniflow_extract().

It appears that miniflow_extract() in emc_processing() spends a lot of
cycles waiting for the packet's data to be read.

Prefetching the next packet's data while parsing removes this delay.
For a single flow pipeline the throughput improves by ~10%.  With a
more realistic pipeline the change has a much smaller effect (~0.5%
improvement)

Signed-off-by: Daniele Di Proietto <diproiettod@vmware.com>
Signed-off-by: Ethan Jackson <ethan@nicira.com>
Acked-by: Ethan Jackson <ethan@nicira.com>

diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
index 5b82c8b..f13169c 100644 (file)
--- a/lib/dpif-netdev.c
+++ b/lib/dpif-netdev.c
@@ -3150,6 +3150,11 @@ emc_processing(struct dp_netdev_pmd_thread *pmd, struct dp_packet **packets,
             continue;
         }
 
+        if (i != cnt - 1) {
+            /* Prefetch next packet data */
+            OVS_PREFETCH(dp_packet_data(packets[i+1]));
+        }
+
         miniflow_extract(packets[i], &key.mf);
         key.len = 0; /* Not computed yet. */
         key.hash = dpif_netdev_packet_get_rss_hash(packets[i], &key.mf);