Re: [dpdk-stable] [PATCH 19.11] net/netvsc: disable external mbuf on Rx by default

[Luca Boccassi <bluca@debian.org>]

On Wed, 2020-12-16 at 10:27 -0800, Long Li wrote:
> From: Long Li <longli@microsoft.com>
> 
> [ upstream commit 096b31fc0d8c989cc455c35f4d1def24a4ed6dee ]
> 
> The upstream commit introduces a new driver parameter and disable the use
> of external mbuf by default. The same can be done by defining a max value
> for the RX threshold for external mbuf.
> 
> The use of external mbuf is disabled by default for two reasons:
>     1. Due to the limitation of the kernel UIO implementation, physical
>        address of this external buffer is not exposed to the user-mode. If
>        this mbuf is passed to another driver, the other driver is unable to
>        map this buffer to iova.
>     2. Some DPDK applications are not aware of external mbuf, and may bug
>        when they receive an mbuf with external buffer attached.
> 
> Signed-off-by: Long Li <longli@microsoft.com>
> ---
>  drivers/net/netvsc/hn_rxtx.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/netvsc/hn_rxtx.c b/drivers/net/netvsc/hn_rxtx.c
> index 19f00a0..d618c17 100644
> --- a/drivers/net/netvsc/hn_rxtx.c
> +++ b/drivers/net/netvsc/hn_rxtx.c
> @@ -42,7 +42,7 @@
>  #define HN_TXD_CACHE_SIZE	32 /* per cpu tx_descriptor pool cache */
>  #define HN_TXCOPY_THRESHOLD	512
>  
> -#define HN_RXCOPY_THRESHOLD	256
> +#define HN_RXCOPY_THRESHOLD	UINT_MAX
>  #define HN_RXQ_EVENT_DEFAULT	2048
>  
>  struct hn_rxinfo {

Thank you - given the widespread breakage, adding this workaround in
19.11 looks like a good solution to me. It has been tested by QA
already, so applied.

-- 
Kind regards,
Luca Boccassi