Re: [PATCH net-next 3/6] net: mvneta: update mb bit before passing the xdp buffer to eBPF layer

On Aug 20, Maciej Fijalkowski wrote:

On Wed, Aug 19, 2020 at 03:13:48PM +0200, Lorenzo Bianconi wrote:

quoted

Update multi-buffer bit (mb) in xdp_buff to notify XDP/eBPF layer and
XDP remote drivers if this is a "non-linear" XDP buffer

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
 drivers/net/ethernet/marvell/mvneta.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
index 832bbb8b05c8..36a3defa63fa 100644
--- a/drivers/net/ethernet/marvell/mvneta.c
+++ b/drivers/net/ethernet/marvell/mvneta.c

@@ -2170,11 +2170,14 @@ mvneta_run_xdp(struct mvneta_port *pp, struct mvneta_rx_queue *rxq,
 	       struct bpf_prog *prog, struct xdp_buff *xdp,
 	       u32 frame_sz, struct mvneta_stats *stats)
 {
+	struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
 	unsigned int len, data_len, sync;
 	u32 ret, act;
 
 	len = xdp->data_end - xdp->data_hard_start - pp->rx_offset_correction;
 	data_len = xdp->data_end - xdp->data;
+
+	xdp->mb = !!sinfo->nr_frags;

But this set is not utilizing it from BPF side in any way. Personally I
would like to see this as a part of work where BPF program would actually
be taught how to rely on xdp->mb. Especially after John's comment in other
patch.

Sameeh is working on them. I did not include the patches since IMO they are
not strictly related to this series. I will include Sameeh's patches in v2.

Regards,
Lorenzo

quoted

 	act = bpf_prog_run_xdp(prog, xdp);
 
 	/* Due xdp_adjust_tail: DMA sync for_device cover max len CPU touch */
-- 
2.26.2