netdev - [PATCH v2 bpf-next 04/14] ixgbe: xsk: decorate IXGBE_XDP

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Date:   Wed, 13 Apr 2022 17:30:05 +0200
From:   Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To:     bpf@...r.kernel.org, ast@...nel.org, daniel@...earbox.net
Cc:     netdev@...r.kernel.org, magnus.karlsson@...el.com,
        alexandr.lobakin@...el.com, maximmi@...dia.com, kuba@...nel.org,
        bjorn@...nel.org,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>
Subject: [PATCH v2 bpf-next 04/14] ixgbe: xsk: decorate IXGBE_XDP_REDIR with likely()

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@...hat.com>
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@...el.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