[PATCH v2 bpf-next 04/14] ixgbe: xsk: decorate IXGBE_XDP_REDIR with likely()

Maciej Fijalkowski
2022-04-13T15:30:45Z

ixgbe_run_xdp_zc() suggests to compiler that XDP_REDIRECT is the most
probable action returned from BPF program that AF_XDP has in its
pipeline. Let's also bring this suggestion up to the callsite of
ixgbe_run_xdp_zc() so that compiler will be able to generate more
optimized code which in turn will make branch predictor happy.

Suggested-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
---
drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c | 25 ++++++++++----------
1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
index dd7ff66d422f..85497bf10624 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
@@ -303,21 +303,22 @@ int ixgbe_clean_rx_irq_zc(struct ixgbe_q_vector *q_vector,
xsk_buff_dma_sync_for_cpu(bi->xdp, rx_ring->xsk_pool);
xdp_res = ixgbe_run_xdp_zc(adapter, rx_ring, bi->xdp);

- if (xdp_res) {
- if (xdp_res & (IXGBE_XDP_TX | IXGBE_XDP_REDIR))
- xdp_xmit |= xdp_res;
- else
- xsk_buff_free(bi->xdp);
+ if (likely(xdp_res & (IXGBE_XDP_TX | IXGBE_XDP_REDIR)))
+ xdp_xmit |= xdp_res;
+ else if (xdp_res == IXGBE_XDP_CONSUMED)
+ xsk_buff_free(bi->xdp);
+ else
+ goto construct_skb;

- bi->xdp = NULL;
- total_rx_packets++;
- total_rx_bytes += size;
+ bi->xdp = NULL;
+ total_rx_packets++;
+ total_rx_bytes += size;

- cleaned_count++;
- ixgbe_inc_ntc(rx_ring);
- continue;
- }
+ cleaned_count++;
+ ixgbe_inc_ntc(rx_ring);
+ continue;

+construct_skb:
/* XDP_PASS path */
skb = ixgbe_construct_skb_zc(rx_ring, bi->xdp);
if (!skb) {
--
2.33.1