On Thu, Jan 25, 2024 at 8:54 PM wangyunjian [off-list ref] wrote:

quoted

-----Original Message-----
From: Jason Wang [mailto:jasowang@redhat.com]
Sent: Thursday, January 25, 2024 12:49 PM
To: wangyunjian <redacted>
Cc: mst@redhat.com; willemdebruijn.kernel@gmail.com; kuba@kernel.org;
davem@davemloft.net; magnus.karlsson@intel.com; netdev@vger.kernel.org;
linux-kernel@vger.kernel.org; kvm@vger.kernel.org;
virtualization@lists.linux.dev; xudingke [off-list ref]
Subject: Re: [PATCH net-next 2/2] tun: AF_XDP Rx zero-copy support

On Wed, Jan 24, 2024 at 5:38 PM Yunjian Wang [off-list ref]
wrote:

quoted

Now the zero-copy feature of AF_XDP socket is supported by some
drivers, which can reduce CPU utilization on the xdp program.
This patch set allows tun to support AF_XDP Rx zero-copy feature.

This patch tries to address this by:
- Use peek_len to consume a xsk->desc and get xsk->desc length.
- When the tun support AF_XDP Rx zero-copy, the vq's array maybe empty.
So add a check for empty vq's array in vhost_net_buf_produce().
- add XDP_SETUP_XSK_POOL and ndo_xsk_wakeup callback support
- add tun_put_user_desc function to copy the Rx data to VM

Code explains themselves, let's explain why you need to do this.

1) why you want to use peek_len
2) for "vq's array", what does it mean?
3) from the view of TUN/TAP tun_put_user_desc() is the TX path, so I guess you
meant TX zerocopy instead of RX (as I don't see codes for
RX?)

OK, I agree and use TX zerocopy instead of RX zerocopy. I meant RX zerocopy
from the view of vhost-net.

Ok.

quoted

A big question is how could you handle GSO packets from userspace/guests?

Now by disabling VM's TSO and csum feature.

Btw, how could you do that?

Thanks