From: Daniele Di Proietto <diproiettod@vmware.com>
Date: Mon, 15 Jun 2015 18:06:39 +0000 (+0100)
Subject: dpif-netdev: Prefetch next packet before miniflow_extract().
X-Git-Tag: v2.4.0~91
X-Git-Url: http://git.cascardo.info/?a=commitdiff_plain;ds=sidebyside;h=72a5e2b8fc8c7c316c0b9feb96b7be5b19265c7c;p=cascardo%2Fovs.git

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 5b82c8b63..f13169c14 100644
--- 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);