Re: [PATCHv12 bpf-next 1/6] bpf: run devmap xdp_prog on flush instead of bulk enqueue

David Ahern
2020-12-17T16:07:49Z

On 12/16/20 7:30 AM, Hangbin Liu wrote:
> @@ -327,40 +328,92 @@ bool dev_map_can_have_prog(struct bpf_map *map)
> return false;
> }
>
> +static int dev_map_bpf_prog_run(struct bpf_prog *xdp_prog,
> + struct xdp_frame **frames, int n,
> + struct net_device *dev)
> +{
> + struct xdp_txq_info txq = { .dev = dev };
> + struct xdp_buff xdp;
> + int i, nframes = 0;
> +
> + for (i = 0; i < n; i++) {
> + struct xdp_frame *xdpf = frames[i];
> + u32 act;
> + int err;
> +
> + xdp_convert_frame_to_buff(xdpf, &xdp);
> + xdp.txq = &txq;
> +
> + act = bpf_prog_run_xdp(xdp_prog, &xdp);
> + switch (act) {
> + case XDP_PASS:
> + err = xdp_update_frame_from_buff(&xdp, xdpf);
> + if (unlikely(err < 0))
> + xdp_return_frame_rx_napi(xdpf);
> + else
> + frames[nframes++] = xdpf;
> + break;
> + default:
> + bpf_warn_invalid_xdp_action(act);
> + fallthrough;
> + case XDP_ABORTED:
> + trace_xdp_exception(dev, xdp_prog, act);
> + fallthrough;
> + case XDP_DROP:
> + xdp_return_frame_rx_napi(xdpf);
> + break;
> + }
> + }
> + return n - nframes; /* dropped frames count */

just return nframes here, since ...

> +}
> +
> static void bq_xmit_all(struct xdp_dev_bulk_queue *bq, u32 flags)
> {
> struct net_device *dev = bq->dev;
> int sent = 0, drops = 0, err = 0;
> + unsigned int cnt = bq->count;
> + unsigned int xdp_drop;
> int i;
>
> - if (unlikely(!bq->count))
> + if (unlikely(!cnt))
> return;
>
> - for (i = 0; i < bq->count; i++) {
> + for (i = 0; i < cnt; i++) {
> struct xdp_frame *xdpf = bq->q[i];
>
> prefetch(xdpf);
> }
>
> - sent = dev->netdev_ops->ndo_xdp_xmit(dev, bq->count, bq->q, flags);
> + if (unlikely(bq->xdp_prog)) {
> + xdp_drop = dev_map_bpf_prog_run(bq->xdp_prog, bq->q, cnt, dev);
> + cnt -= xdp_drop;

... that is apparently what you really want.

> + if (!cnt) {
> + sent = 0;
> + drops = xdp_drop;
> + goto out;
> + }
> + }
> +
> + sent = dev->netdev_ops->ndo_xdp_xmit(dev, cnt, bq->q, flags);
> if (sent < 0) {
> err = sent;
> sent = 0;
> goto error;
> }
> - drops = bq->count - sent;
> + drops = (cnt - sent) + xdp_drop;
> out:
> bq->count = 0;
>
> trace_xdp_devmap_xmit(bq->dev_rx, dev, sent, drops, err);
> bq->dev_rx = NULL;
> + bq->xdp_prog = NULL;
> __list_del_clearprev(&bq->flush_node);
> return;
> error:
> /* If ndo_xdp_xmit fails with an errno, no frames have been
> * xmit'ed and it's our responsibility to them free all.
> */
> - for (i = 0; i < bq->count; i++) {
> + for (i = 0; i < cnt; i++) {
> struct xdp_frame *xdpf = bq->q[i];
>
> xdp_return_frame_rx_napi(xdpf);
> @@ -408,7 +461,8 @@ struct bpf_dtab_netdev *__dev_map_lookup_elem(struct bpf_map *map, u32 key)
> * Thus, safe percpu variable access.
> */
> static void bq_enqueue(struct net_device *dev, struct xdp_frame *xdpf,
> - struct net_device *dev_rx)
> + struct net_device *dev_rx,
> + struct bpf_dtab_netdev *dst)
> {
> struct list_head *flush_list = this_cpu_ptr(&dev_flush_list);
> struct xdp_dev_bulk_queue *bq = this_cpu_ptr(dev->xdp_bulkq);
> @@ -423,6 +477,14 @@ static void bq_enqueue(struct net_device *dev, struct xdp_frame *xdpf,
> if (!bq->dev_rx)
> bq->dev_rx = dev_rx;
>
> + /* Store (potential) xdp_prog that run before egress to dev as
> + * part of bulk_queue. This will be same xdp_prog for all
> + * xdp_frame's in bulk_queue, because this per-CPU store must
> + * be flushed from net_device drivers NAPI func end.
> + */
> + if (dst && dst->xdp_prog && !bq->xdp_prog)
> + bq->xdp_prog = dst->xdp_prog;

if you pass in xdp_prog through __xdp_enqueue you can reduce that to just:

if (!bq->xdp_prog)
bq->xdp_prog = xdp_prog;

> bq->q[bq->count++] = xdpf;
>
> if (!bq->flush_node.prev)
> @@ -430,7 +492,8 @@ static void bq_enqueue(struct net_device *dev, struct xdp_frame *xdpf,
> }
>
> static inline int __xdp_enqueue(struct net_device *dev, struct xdp_buff *xdp,
> - struct net_device *dev_rx)
> + struct net_device *dev_rx,
> + struct bpf_dtab_netdev *dst)
> {
> struct xdp_frame *xdpf;
> int err;
> @@ -446,42 +509,14 @@ static inline int __xdp_enqueue(struct net_device *dev, struct xdp_buff *xdp,
> if (unlikely(!xdpf))
> return -EOVERFLOW;
>
> - bq_enqueue(dev, xdpf, dev_rx);
> + bq_enqueue(dev, xdpf, dev_rx, dst);
> return 0;
> }
>
> -static struct xdp_buff *dev_map_run_prog(struct net_device *dev,
> - struct xdp_buff *xdp,
> - struct bpf_prog *xdp_prog)
> -{
> - struct xdp_txq_info txq = { .dev = dev };
> - u32 act;
> -
> - xdp_set_data_meta_invalid(xdp);
> - xdp->txq = &txq;
> -
> - act = bpf_prog_run_xdp(xdp_prog, xdp);
> - switch (act) {
> - case XDP_PASS:
> - return xdp;
> - case XDP_DROP:
> - break;
> - default:
> - bpf_warn_invalid_xdp_action(act);
> - fallthrough;
> - case XDP_ABORTED:
> - trace_xdp_exception(dev, xdp_prog, act);
> - break;
> - }
> -
> - xdp_return_buff(xdp);
> - return NULL;
> -}
> -
> int dev_xdp_enqueue(struct net_device *dev, struct xdp_buff *xdp,
> struct net_device *dev_rx)
> {
> - return __xdp_enqueue(dev, xdp, dev_rx);
> + return __xdp_enqueue(dev, xdp, dev_rx, NULL);
> }
>
> int dev_map_enqueue(struct bpf_dtab_netdev *dst, struct xdp_buff *xdp,
> @@ -489,12 +524,7 @@ int dev_map_enqueue(struct bpf_dtab_netdev *dst, struct xdp_buff *xdp,
> {
> struct net_device *dev = dst->dev;
>
> - if (dst->xdp_prog) {
> - xdp = dev_map_run_prog(dev, xdp, dst->xdp_prog);
> - if (!xdp)
> - return 0;
> - }
> - return __xdp_enqueue(dev, xdp, dev_rx);
> + return __xdp_enqueue(dev, xdp, dev_rx, dst);
> }
>
> int dev_map_generic_redirect(struct bpf_dtab_netdev *dst, struct sk_buff *skb,
>