[Devel] [PATCH RHEL7 COMMIT] vhost-net: enable zerocopy tx by default

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-327.36.1.vz7.19.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-327.36.1.vz7.19.3
------>
commit 6a6f8f41ce77fcda938d8b924bdc8f71a2f7510d
Author: Michael S. Tsirkin <mst at redhat.com>
Date:   Mon Oct 24 16:15:19 2016 +0400

    vhost-net: enable zerocopy tx by default
    
    Zero copy TX has been around for a while now.
    We seem to be down to eliminating theoretical bugs
    and performance tuning at this point:
    it's probably time to enable it by default so that
    most users get the benefit.
    
    Keep the flag around meanwhile so users can experiment
    with disabling this if they experience regressions.
    I expect that we will remove it in the future.
    
    Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
    (cherry picked from commit f9611c43ab0ddaf547b395c90fb842f55959334c)
    
    Re-apply this on top of RHEL7 reverting it in 3.10.0-98.el7 by a patch
    whose changelog entry reads:
    
    [virt] vhost/net: disable zero copy by default (Jason Wang)[1069045]
    
    Note that Fedora kernels never had this flag reversed and seem to be
    fine.
    
    Signed-off-by: Roman Kagan <rkagan at virtuozzo.com>
    
    Note: investigation of PSBM-52390 eventually revealed the root cause for the tx
    stalls, which happens to be unrelated to zerocopy. Nonetheless zerocopy is
    supposedly a performance improvement so we'd like to include it in vzkernel.
---
 drivers/vhost/net.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 2c42414..27e9c86 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -30,7 +30,7 @@
 
 #include "vhost.h"
 
-static int experimental_zcopytx;
+static int experimental_zcopytx = 1;
 module_param(experimental_zcopytx, int, 0444);
 MODULE_PARM_DESC(experimental_zcopytx, "Enable Zero Copy TX;"
 		                       " 1 -Enable; 0 - Disable");