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

Hangbin Liu
2020-12-21T08:39:41Z

Hi David,

I just aware that,
On Thu, Dec 17, 2020 at 09:07:03AM -0700, David Ahern wrote:
> > +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 ...

If we return nframes here,
>
> > +}
> > +
> > 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.

then this will be

cnt = dev_map_bpf_prog_run(bq->xdp_prog, bq->q, cnt, dev);
xdp_drop = bq->count - cnt;

So there is no much difference whether we return passed frames or dropped
frames.
>
> > + if (!cnt) {
> > + sent = 0;
> > + drops = xdp_drop;
> > + goto out;
> > + }
> > + }

Thanks
Hangbin