On Thu, Dec 08, 2016 at 10:18:22AM -0800, John Fastabend wrote: > On 16-12-07 10:11 PM, Michael S. Tsirkin wrote: > > On Wed, Dec 07, 2016 at 12:12:45PM -0800, John Fastabend wrote: > >> This adds support for the XDP_TX action to virtio_net. When an XDP > >> program is run and returns the XDP_TX action the virtio_net XDP > >> implementation will transmit the packet on a TX queue that aligns > >> with the current CPU that the XDP packet was processed on. > >> > >> Before sending the packet the header is zeroed. Also XDP is expected > >> to handle checksum correctly so no checksum offload support is > >> provided. > >> > >> Signed-off-by: John Fastabend <john.r.fastab...@intel.com> > >> --- > >> drivers/net/virtio_net.c | 99 > >> +++++++++++++++++++++++++++++++++++++++++++--- > >> 1 file changed, 92 insertions(+), 7 deletions(-) > >> > >> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > >> index 28b1196..8e5b13c 100644 > >> --- a/drivers/net/virtio_net.c > >> +++ b/drivers/net/virtio_net.c > >> @@ -330,12 +330,57 @@ static struct sk_buff *page_to_skb(struct > >> virtnet_info *vi, > >> return skb; > >> } > >> > >> +static void virtnet_xdp_xmit(struct virtnet_info *vi, > >> + struct receive_queue *rq, > >> + struct send_queue *sq, > >> + struct xdp_buff *xdp) > >> +{ > >> + struct page *page = virt_to_head_page(xdp->data); > >> + struct virtio_net_hdr_mrg_rxbuf *hdr; > >> + unsigned int num_sg, len; > >> + void *xdp_sent; > >> + int err; > >> + > >> + /* Free up any pending old buffers before queueing new ones. */ > >> + while ((xdp_sent = virtqueue_get_buf(sq->vq, &len)) != NULL) { > >> + struct page *sent_page = virt_to_head_page(xdp_sent); > >> + > >> + if (vi->mergeable_rx_bufs) > >> + put_page(sent_page); > >> + else > >> + give_pages(rq, sent_page); > >> + } > > > > Looks like this is the only place where you do virtqueue_get_buf. > > No interrupt handler? > > This means that if you fill up the queue, nothing will clean it > > and things will get stuck. > > hmm OK so the callbacks should be implemented to do this and a pair > of virtqueue_enable_cb_prepare()/virtqueue_disable_cb() used to enable > and disable callbacks if packets are enqueued.
Oh I didn't realize XDP never stops processing packets, even if they are never freed. In that case you do not need callbacks. > Also in the normal xmit path via start_xmit() will the same condition > happen? It looks like free_old_xmit_skbs for example is only called if > a packet is sent could we end up holding on to skbs in this case? I > don't see free_old_xmit_skbs being called from any callbacks? Right - all it does is restart the queue. That's why we don't support BQL right now. > > Can this be the issue you saw? > > nope see below I was mishandling the big_packets page cleanup path in > the error case. > > > > > > >> + > >> + /* Zero header and leave csum up to XDP layers */ > >> + hdr = xdp->data; > >> + memset(hdr, 0, vi->hdr_len); > >> + > >> + nu_sg = 1; > >> + sg_init_one(sq->sg, xdp->data, xdp->data_end - xdp->data); > >> + err = virtqueue_add_outbuf(sq->vq, sq->sg, num_sg, > >> + xdp->data, GFP_ATOMIC); > >> + if (unlikely(err)) { > >> + if (vi->mergeable_rx_bufs) > >> + put_page(page); > >> + else > >> + give_pages(rq, page); > >> + } else if (!vi->mergeable_rx_bufs) { > >> + /* If not mergeable bufs must be big packets so cleanup pages */ > >> + give_pages(rq, (struct page *)page->private); > >> + page->private = 0; > >> + } > >> + > >> + virtqueue_kick(sq->vq); > > > > Is this unconditional kick a work-around for hang > > we could not figure out yet? > > I tracked the original issue down to how I handled the big_packet page > cleanups. > > > I guess this helps because it just slows down the guest. > > I don't much like it ... > > I left it like this copying the pattern in balloon and input drivers. I > can change it back to the previous pattern where it is only called if > there is no errors. It has been running fine with the old pattern now > for an hour or so. > > .John OK makes sense.