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

Hi David,

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

quoted

+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,

quoted

+}
+
 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.

quoted

+		if (!cnt) {
+			sent = 0;
+			drops = xdp_drop;
+			goto out;
+		}
+	}

Thanks
Hangbin