From: PiotrX Kleski <piotrx.kleski@intel.com>
Date: Wed, 9 Dec 2020 13:32:26 +0000 (+0100)
Subject: ip: ip4 rewrite prefetch optimization
X-Git-Tag: v21.06-rc0~23
X-Git-Url: https://gerrit.fd.io/r/gitweb?a=commitdiff_plain;h=refs%2Fchanges%2F69%2F30369%2F2;p=vpp.git

ip: ip4 rewrite prefetch optimization

Type: improvement

ip4_rewrite_inline_with_gso() did vlib_prefetch_buffer_header() for all nodes.
However it is not necessary for ip-rewrite, it is only needed by ip-midchain.

This patch makes ip4-rewrite prefetches less buffers to save cycles.

Signed-off-by: PiotrX Kleski <piotrx.kleski@intel.com>
Change-Id: Ib82dcb0eda4a2d1d7b8d664f2224d49b72aef50f
---

diff --git a/src/vnet/ip/ip4_forward.c b/src/vnet/ip/ip4_forward.c
index fdc92ca16f8..77ea4c5524e 100644
--- a/src/vnet/ip/ip4_forward.c
+++ b/src/vnet/ip/ip4_forward.c
@@ -2109,8 +2109,11 @@ ip4_rewrite_inline_with_gso (vlib_main_t * vm,
       u32 tx_sw_if_index0, tx_sw_if_index1;
       u8 *p;
 
-      vlib_prefetch_buffer_header (b[6], LOAD);
-      vlib_prefetch_buffer_header (b[7], LOAD);
+      if (is_midchain)
+	{
+	  vlib_prefetch_buffer_header (b[6], LOAD);
+	  vlib_prefetch_buffer_header (b[7], LOAD);
+	}
 
       adj_index0 = vnet_buffer (b[0])->ip.adj_index[VLIB_TX];
       adj_index1 = vnet_buffer (b[1])->ip.adj_index[VLIB_TX];