From: Jason Wang <jasowang@redhat.com>
Date: Mon, 17 Jun 2019 09:20:54 +0000 (-0400)
Subject: vhost_net: disable zerocopy by default
X-Git-Tag: Ubuntu-4.15.0-61.68~737
X-Git-Url: https://git.proxmox.com/?p=mirror_ubuntu-bionic-kernel.git;a=commitdiff_plain;h=b15cf44eb64e1505e2e7c8a104f00758286982aa

vhost_net: disable zerocopy by default

BugLink: https://bugs.launchpad.net/bugs/1839036

[ Upstream commit 098eadce3c622c07b328d0a43dda379b38cf7c5e ]

Vhost_net was known to suffer from HOL[1] issues which is not easy to
fix. Several downstream disable the feature by default. What's more,
the datapath was split and datacopy path got the support of batching
and XDP support recently which makes it faster than zerocopy part for
small packets transmission.

It looks to me that disable zerocopy by default is more
appropriate. It cold be enabled by default again in the future if we
fix the above issues.

[1] https://patchwork.kernel.org/patch/3787671/

Signed-off-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
---

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index a23c7e7c1652..e71583c96055 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -35,7 +35,7 @@
 
 #include "vhost.h"
 
-static int experimental_zcopytx = 1;
+static int experimental_zcopytx = 0;
 module_param(experimental_zcopytx, int, 0444);
 MODULE_PARM_DESC(experimental_zcopytx, "Enable Zero Copy TX;"
 		                       " 1 -Enable; 0 - Disable");