linux-kernel - [PATCH net-next] igc: Fix TX drops in XDP ZC

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Message-Id: <20250319-igc-fix-tx-zero-copy-drops-v1-1-d90bc63a4dc4@siemens.com>
Date: Wed, 19 Mar 2025 15:18:48 +0100
From: Zdenek Bouska <zdenek.bouska@...mens.com>
To: Tony Nguyen <anthony.l.nguyen@...el.com>, 
 Przemek Kitszel <przemyslaw.kitszel@...el.com>, 
 Andrew Lunn <andrew+netdev@...n.ch>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
 Jesper Dangaard Brouer <hawk@...nel.org>, 
 John Fastabend <john.fastabend@...il.com>, 
 Andre Guedes <andre.guedes@...el.com>, 
 Vedang Patel <vedang.patel@...el.com>, 
 Maciej Fijalkowski <maciej.fijalkowski@...el.com>, 
 Jithu Joseph <jithu.joseph@...el.com>, 
 Song Yoong Siang <yoong.siang.song@...el.com>, 
 Florian Bezdeka <florian.bezdeka@...mens.com>
Cc: intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org, 
 linux-kernel@...r.kernel.org, bpf@...r.kernel.org, 
 Zdenek Bouska <zdenek.bouska@...mens.com>
Subject: [PATCH net-next] igc: Fix TX drops in XDP ZC

Fixes TX frame drops in AF_XDP zero copy mode when budget < 4.
xsk_tx_peek_desc() consumed TX frame and it was ignored because of
low budget. Not even AF_XDP completion was done for dropped frames.

It can be reproduced on i226 by sending 100000x 60 B frames with
launch time set to minimal IPG (672 ns between starts of frames)
on 1Gbit/s. Always 1026 frames are not sent and are missing a
completion.

Fixes: 9acf59a752d4c ("igc: Enable TX via AF_XDP zero-copy")
Signed-off-by: Zdenek Bouska <zdenek.bouska@...mens.com>
---
 drivers/net/ethernet/intel/igc/igc_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index 472f009630c9..f2e0a30a3497 100644
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -3042,7 +3042,7 @@ static void igc_xdp_xmit_zc(struct igc_ring *ring)
 	 * descriptors. Therefore, to be safe, we always ensure we have at least
 	 * 4 descriptors available.
 	 */
-	while (xsk_tx_peek_desc(pool, &xdp_desc) && budget >= 4) {
+	while (budget >= 4 && xsk_tx_peek_desc(pool, &xdp_desc)) {
 		struct igc_metadata_request meta_req;
 		struct xsk_tx_metadata *meta = NULL;
 		struct igc_tx_buffer *bi;

---
base-commit: 8ef890df4031121a94407c84659125cbccd3fdbe
change-id: 20250310-igc-fix-tx-zero-copy-drops-1c4a81441033

Best regards,
-- 
Zdenek Bouska

Siemens, s.r.o.
Foundational Technologies