Linux Virtualization - Jun 2019 - [PATCH net-next] vhost_net: disable zerocopy by default

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 at redhat.com>
---
 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 2d9df786a9d3..21e0805e5e60 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -36,7 +36,7 @@
 
 #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");
-- 
2.18.1

On Mon, Jun 17, 2019 at 05:20:54AM -0400, Jason Wang
wrote:
> 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 at redhat.com>

Acked-by: Michael S. Tsirkin <mst at redhat.com>
> ---
>  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 2d9df786a9d3..21e0805e5e60 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -36,7 +36,7 @@
>  
>  #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");
> -- 
> 2.18.1

From: Jason Wang <jasowang at redhat.com>
Date: Mon, 17 Jun 2019 05:20:54 -0400
> 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 at redhat.com>
Applied, thanks Jason.