Re: [PATCH net-next v2 3/3] tun: AF_XDP Tx zero-copy support

[Maciej Fijalkowski <maciej.fijalkowski@intel.com>]

On Wed, Feb 28, 2024 at 07:05:56PM +0800, Yunjian Wang wrote:
> This patch set allows TUN to support the AF_XDP Tx zero-copy feature,
> which can significantly reduce CPU utilization for XDP programs.

Why no Rx ZC support though? What will happen if I try rxdrop xdpsock
against tun with this patch? You clearly allow for that.

> 
> Since commit fc72d1d54dd9 ("tuntap: XDP transmission"), the pointer
> ring has been utilized to queue different types of pointers by encoding
> the type into the lower bits. Therefore, we introduce a new flag,
> TUN_XDP_DESC_FLAG(0x2UL), which allows us to enqueue XDP descriptors
> and differentiate them from XDP buffers and sk_buffs. Additionally, a
> spin lock is added for enabling and disabling operations on the xsk pool.
> 
> The performance testing was performed on a Intel E5-2620 2.40GHz machine.
> Traffic were generated/send through TUN(testpmd txonly with AF_XDP)
> to VM (testpmd rxonly in guest).
> 
> +------+---------+---------+---------+
> |      |   copy  |zero-copy| speedup |
> +------+---------+---------+---------+
> | UDP  |   Mpps  |   Mpps  |    %    |
> | 64   |   2.5   |   4.0   |   60%   |
> | 512  |   2.1   |   3.6   |   71%   |
> | 1024 |   1.9   |   3.3   |   73%   |
> +------+---------+---------+---------+
> 
> Signed-off-by: Yunjian Wang <wangyunjian@huawei.com>
> ---
>  drivers/net/tun.c      | 177 +++++++++++++++++++++++++++++++++++++++--
>  drivers/vhost/net.c    |   4 +
>  include/linux/if_tun.h |  32 ++++++++
>  3 files changed, 208 insertions(+), 5 deletions(-)
>