netdev - [PATCH bpf 2/4] ice: xsk: eliminate unnecessary loop iteration

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Date:   Mon, 28 Mar 2022 16:21:21 +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, bjorn@...nel.org
Subject: [PATCH bpf 2/4] ice: xsk: eliminate unnecessary loop iteration

From: Magnus Karlsson <magnus.karlsson@...el.com>

The NIC Tx ring completion routine cleans entries from the ring in
batches. However, it processes one more batch than it is supposed
to. Note that this does not matter from a functionality point of view
since it will not find a set DD bit for the next batch and just exit
the loop. But from a performance perspective, it is faster to
terminate the loop before and not issue an expensive read over PCIe to
get the DD bit.

Fixes: 126cdfe1007a ("ice: xsk: Improve AF_XDP ZC Tx and use batching API")
Signed-off-by: Magnus Karlsson <magnus.karlsson@...el.com>
---
 drivers/net/ethernet/intel/ice/ice_xsk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/intel/ice/ice_xsk.c b/drivers/net/ethernet/intel/ice/ice_xsk.c
index 88853a6ed931..51427cb4971a 100644
--- a/drivers/net/ethernet/intel/ice/ice_xsk.c
+++ b/drivers/net/ethernet/intel/ice/ice_xsk.c
@@ -754,7 +754,7 @@ static u16 ice_clean_xdp_irq_zc(struct ice_tx_ring *xdp_ring, int napi_budget)
 		next_dd = next_dd + tx_thresh;
 		if (next_dd >= desc_cnt)
 			next_dd = tx_thresh - 1;
-	} while (budget--);
+	} while (--budget);
 
 	xdp_ring->next_dd = next_dd;
 
-- 
2.27.0