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Date: Fri, 8 May 2020 14:07:04 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Denis Kirjanov <kda@...ux-powerpc.org>
Cc: netdev@...r.kernel.org, brouer@...hat.com, jgross@...e.com,
wei.liu@...nel.org, paul@....org, ilias.apalodimas@...aro.org
Subject: Re: [PATCH net-next v8 1/3] xen networking: add basic XDP support
for xen-netfront
On Thu, 7 May 2020 15:40:39 +0300 Denis Kirjanov wrote:
> The patch adds a basic XDP processing to xen-netfront driver.
>
> We ran an XDP program for an RX response received from netback
> driver. Also we request xen-netback to adjust data offset for
> bpf_xdp_adjust_head() header space for custom headers.
>
> synchronization between frontend and backend parts is done
> by using xenbus state switching:
> Reconfiguring -> Reconfigured- > Connected
>
> UDP packets drop rate using xdp program is around 310 kpps
> using ./pktgen_sample04_many_flows.sh and 160 kpps without the patch.
Please provide a cover letter for the submission.
> @@ -167,6 +179,9 @@ struct netfront_rx_info {
> struct xen_netif_extra_info extras[XEN_NETIF_EXTRA_TYPE_MAX - 1];
> };
>
> +static int xennet_xdp_xmit(struct net_device *dev, int n,
> + struct xdp_frame **frames, u32 flags);
Is it possible to put the function here and avoid the forward
declaration?
> static void skb_entry_set_link(union skb_entry *list, unsigned short id)
> {
> list->link = id;
> @@ -265,8 +280,8 @@ static struct sk_buff *xennet_alloc_one_rx_buffer(struct netfront_queue *queue)
> if (unlikely(!skb))
> return NULL;
>
> - page = alloc_page(GFP_ATOMIC | __GFP_NOWARN);
> - if (!page) {
> + page = page_pool_dev_alloc_pages(queue->page_pool);
> + if (unlikely(!page)) {
> kfree_skb(skb);
> return NULL;
> }
> @@ -778,6 +793,53 @@ static int xennet_get_extras(struct netfront_queue *queue,
> return err;
> }
>
> +u32 xennet_run_xdp(struct netfront_queue *queue, struct page *pdata,
static
> + struct xen_netif_rx_response *rx, struct bpf_prog *prog,
> + struct xdp_buff *xdp)
> +{
> + struct xdp_frame *xdpf;
> + u32 len = rx->status;
> + u32 act = XDP_PASS;
> + int err;
> +
> + xdp->data_hard_start = page_address(pdata);
> + xdp->data = xdp->data_hard_start + XDP_PACKET_HEADROOM;
> + xdp_set_data_meta_invalid(xdp);
> + xdp->data_end = xdp->data + len;
> + xdp->rxq = &queue->xdp_rxq;
> + xdp->handle = 0;
No need to clear this.
> + act = bpf_prog_run_xdp(prog, xdp);
> + switch (act) {
> + case XDP_TX:
> + get_page(pdata);
> + xdpf = convert_to_xdp_frame(xdp);
> + err = xennet_xdp_xmit(queue->info->netdev, 1, &xdpf, 0);
> + if (unlikely(err < 0))
> + trace_xdp_exception(queue->info->netdev, prog, act);
> + break;
> + case XDP_REDIRECT:
> + get_page(pdata);
> + err = xdp_do_redirect(queue->info->netdev, xdp, prog);
> + if (unlikely(err))
> + trace_xdp_exception(queue->info->netdev, prog, act);
> + xdp_do_flush();
Can you call flush after the RX loop? (xennet_poll()?) This is supposed
to batch all redirections in the NAPI cycle.
> + break;
> + case XDP_PASS:
> + case XDP_DROP:
> + break;
> +
> + case XDP_ABORTED:
> + trace_xdp_exception(queue->info->netdev, prog, act);
> + break;
> +
> + default:
> + bpf_warn_invalid_xdp_action(act);
> + }
> +
> + return act;
> +}
> +
> static int xennet_get_responses(struct netfront_queue *queue,
> struct netfront_rx_info *rinfo, RING_IDX rp,
> struct sk_buff_head *list)
> @@ -792,6 +854,9 @@ static int xennet_get_responses(struct netfront_queue *queue,
> int slots = 1;
> int err = 0;
> unsigned long ret;
> + struct bpf_prog *xdp_prog;
> + struct xdp_buff xdp;
> + u32 verdict;
>
> if (rx->flags & XEN_NETRXF_extra_info) {
> err = xennet_get_extras(queue, extras, rp);
> @@ -827,9 +892,20 @@ static int xennet_get_responses(struct netfront_queue *queue,
>
> gnttab_release_grant_reference(&queue->gref_rx_head, ref);
>
> - __skb_queue_tail(list, skb);
> -
> + rcu_read_lock();
> + xdp_prog = rcu_dereference(queue->xdp_prog);
> + if (xdp_prog && !(rx->flags & XEN_NETRXF_more_data)) {
What is XEN_NETRXF_more_data?
If you have a mis-formatted frame it has to be dropped, nothing can
escape the XDP program and go to the stack.
> + /* currently only a single page contains data */
> + WARN_ON_ONCE(skb_shinfo(skb)->nr_frags != 1);
> + verdict = xennet_run_xdp(queue,
> + skb_frag_page(&skb_shinfo(skb)->frags[0]),
> + rx, xdp_prog, &xdp);
> + if (verdict != XDP_PASS)
> + err = -EINVAL;
> + }
> + rcu_read_unlock();
> next:
> + __skb_queue_tail(list, skb);
> if (!(rx->flags & XEN_NETRXF_more_data))
> break;
>
> +static int xennet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
> + struct netlink_ext_ack *extack)
> +{
> + struct netfront_info *np = netdev_priv(dev);
> + struct bpf_prog *old_prog;
> + unsigned int i, err;
> + unsigned long int max_mtu = XEN_PAGE_SIZE - XDP_PACKET_HEADROOM;
> +
> + if (dev->mtu > max_mtu) {
> + netdev_warn(dev, "XDP requires MTU less than %lu\n", max_mtu);
> + return -EINVAL;
> + }
> +
> + if (!np->netback_has_xdp_headroom)
> + return 0;
> +
> + old_prog = rtnl_dereference(np->queues[0].xdp_prog);
> + if (!old_prog && !prog)
You don't have to check this, the core will not call drivers any more
if there is no program and request is to disable XDP.
> + return 0;
> +
> + if (prog)
> + bpf_prog_add(prog, dev->real_num_tx_queues);
> +
> + for (i = 0; i < dev->real_num_tx_queues; ++i)
> + rcu_assign_pointer(np->queues[i].xdp_prog, prog);
I'm I reading this right the moment you assign the program the RX
function will start assuming there is a headroom, even if you haven't
reconfigured the backend, yet..
> + if (old_prog)
> + for (i = 0; i < dev->real_num_tx_queues; ++i)
> + bpf_prog_put(old_prog);
> +
> + xenbus_switch_state(np->xbdev, XenbusStateReconfiguring);
> +
> + err = talk_to_netback_xdp(np, prog ? NETBACK_XDP_HEADROOM_ENABLE:
> + NETBACK_XDP_HEADROOM_DISABLE);
> + if (err)
> + return err;
> +
> + /* avoid race with XDP headroom adjustment */
> + wait_event(module_wq,
> + xenbus_read_driver_state(np->xbdev->otherend) ==
> + XenbusStateReconfigured);
> + np->netfront_xdp_enabled = true;
> + xenbus_switch_state(np->xbdev, XenbusStateConnected);
> +
> + return 0;
> +}
> +
> @@ -1754,6 +1993,51 @@ static void xennet_destroy_queues(struct netfront_info *info)
> info->queues = NULL;
> }
>
> +
> +
> +static int xennet_create_page_pool(struct netfront_queue *queue)
Please run checkpatch --strict on your patches.
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