On Mon, Jan 29, 2024 at 7:10 PM wangyunjian <[email protected]> wrote:
>
> > -----Original Message-----
> > From: Jason Wang [mailto:[email protected]]
> > Sent: Monday, January 29, 2024 11:05 AM
> > To: wangyunjian <[email protected]>
> > Cc: [email protected]; [email protected]; [email protected];
> > [email protected]; [email protected]; [email protected];
> > [email protected]; [email protected];
> > [email protected]; xudingke <[email protected]>
> > Subject: Re: [PATCH net-next 2/2] tun: AF_XDP Rx zero-copy support
> >
> > On Sat, Jan 27, 2024 at 5:34 PM wangyunjian <wangyunjian@huaweicom>
> > wrote:
> > >
> > > > > -----Original Message-----
> > > > > From: Jason Wang [mailto:[email protected]]
> > > > > Sent: Thursday, January 25, 2024 12:49 PM
> > > > > To: wangyunjian <[email protected]>
> > > > > Cc: [email protected]; [email protected];
> > > > > [email protected]; [email protected]; [email protected];
> > > > > [email protected]; [email protected];
> > > > > [email protected]; [email protected]; xudingke
> > > > > <[email protected]>
> > > > > 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
> > > > <[email protected]>
> > > > > wrote:
> > > > > >
> > > > > > 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.
> > > >
> > > > >
> > > > > A big question is how could you handle GSO packets from
> > userspace/guests?
> > > >
> > > > Now by disabling VM's TSO and csum feature. XDP does not support GSO
> > > > packets.
> > > > However, this feature can be added once XDP supports it in the future.
> > > >
> > > > >
> > > > > >
> > > > > > Signed-off-by: Yunjian Wang <[email protected]>
> > > > > > ---
> > > > > > drivers/net/tun.c | 165
> > > > > +++++++++++++++++++++++++++++++++++++++++++-
> > > > > > drivers/vhost/net.c | 18 +++--
> > > > > > 2 files changed, 176 insertions(+), 7 deletions(-)
> > >
> > > [...]
> > >
> > > > > >
> > > > > > static int peek_head_len(struct vhost_net_virtqueue *rvq,
> > > > > > struct sock
> > > > > > *sk) {
> > > > > > + struct socket *sock = sk->sk_socket;
> > > > > > struct sk_buff *head;
> > > > > > int len = 0;
> > > > > > unsigned long flags;
> > > > > >
> > > > > > - if (rvq->rx_ring)
> > > > > > - return vhost_net_buf_peek(rvq);
> > > > > > + if (rvq->rx_ring) {
> > > > > > + len = vhost_net_buf_peek(rvq);
> > > > > > + if (likely(len))
> > > > > > + return len;
> > > > > > + }
> > > > > > +
> > > > > > + if (sock->ops->peek_len)
> > > > > > + return sock->ops->peek_len(sock);
> > > > >
> > > > > What prevents you from reusing the ptr_ring here? Then you don't
> > > > > need the above tricks.
> > > >
> > > > Thank you for your suggestion. I will consider how to reuse the ptr_ring.
> > >
> > > If ptr_ring is used to transfer xdp_descs, there is a problem: After
> > > some xdp_descs are obtained through xsk_tx_peek_desc(), the descs may
> > > fail to be added to ptr_ring. However, no API is available to
> > > implement the rollback function.
> >
> > I don't understand, this issue seems to exist in the physical NIC as well?
> >
> > We get more descriptors than the free slots in the NIC ring.
> >
> > How did other NIC solve this issue?
>
> Currently, physical NICs such as i40e, ice, ixgbe, igc, and mlx5 obtains
> available NIC descriptors and then retrieve the same number of xsk
> descriptors for processing.
Any reason we can't do the same? ptr_ring should be much simpler than
NIC ring anyhow.
Thanks
>
> Thanks
>
> >
> > Thanks
> >
> > >
> > > Thanks
> > >
> > > >
> > > > >
> > > > > Thanks
> > > > >
> > > > >
> > > > > >
> > > > > > spin_lock_irqsave(&sk->sk_receive_queue.lock, flags);
> > > > > > head = skb_peek(&sk->sk_receive_queue);
> > > > > > --
> > > > > > 2.33.0
> > > > > >
> > >
>