On Sat, Dec 19, 2020 at 4:56 PM Shay Agroskin [off-list ref] wrote:

Lorenzo Bianconi [off-list ref] writes:

quoted

Introduce the capability to map non-linear xdp buffer running
mvneta_xdp_submit_frame() for XDP_TX and XDP_REDIRECT

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
 drivers/net/ethernet/marvell/mvneta.c | 94
 ++++++++++++++++-----------
 1 file changed, 56 insertions(+), 38 deletions(-)

[...]

quoted

                      if (napi && buf->type ==
 MVNETA_TYPE_XDP_TX)
                              xdp_return_frame_rx_napi(buf->xdpf);
                      else

@@ -2054,45 +2054,64 @@ mvneta_xdp_put_buff(struct mvneta_port

*pp, struct mvneta_rx_queue *rxq,

 static int
 mvneta_xdp_submit_frame(struct mvneta_port *pp, struct
 mvneta_tx_queue *txq,
-                     struct xdp_frame *xdpf, bool dma_map)
+                     struct xdp_frame *xdpf, int *nxmit_byte,
bool dma_map)
 {
-     struct mvneta_tx_desc *tx_desc;
-     struct mvneta_tx_buf *buf;
-     dma_addr_t dma_addr;
+     struct xdp_shared_info *xdp_sinfo =
xdp_get_shared_info_from_frame(xdpf);
+     int i, num_frames = xdpf->mb ? xdp_sinfo->nr_frags + 1 :
1;
+     struct mvneta_tx_desc *tx_desc = NULL;
+     struct page *page;

-     if (txq->count >= txq->tx_stop_threshold)
+     if (txq->count + num_frames >= txq->size)
              return MVNETA_XDP_DROPPED;

-     tx_desc = mvneta_txq_next_desc_get(txq);
+     for (i = 0; i < num_frames; i++) {
+             struct mvneta_tx_buf *buf =
&txq->buf[txq->txq_put_index];
+             skb_frag_t *frag = i ? &xdp_sinfo->frags[i - 1] :
NULL;
+             int len = frag ? xdp_get_frag_size(frag) :
xdpf->len;

nit, from branch prediction point of view, maybe it would be
better to write
     int len = i ? xdp_get_frag_size(frag) : xdpf->len;

ack, I will fix it in v6.

Regards,
Lorenzo

since the value of i is checked one line above
Disclaimer: I'm far from a compiler expert, and don't know whether
the compiler would know to group these two assignments together
into a single branch prediction decision, but it feels like using
'i' would make this decision easier for it.

Thanks,
Shay

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