netdev - [PATCH net 2/5] igc: Fix TX drops in XDP ZC

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Message-ID: <20250402173900.1957261-3-anthony.l.nguyen@intel.com>
Date: Wed,  2 Apr 2025 10:38:54 -0700
From: Tony Nguyen <anthony.l.nguyen@...el.com>
To: davem@...emloft.net,
	kuba@...nel.org,
	pabeni@...hat.com,
	edumazet@...gle.com,
	andrew+netdev@...n.ch,
	netdev@...r.kernel.org
Cc: Zdenek Bouska <zdenek.bouska@...mens.com>,
	anthony.l.nguyen@...el.com,
	vitaly.lifshits@...el.com,
	dima.ruinskiy@...el.com,
	maciej.fijalkowski@...el.com,
	magnus.karlsson@...el.com,
	ast@...nel.org,
	daniel@...earbox.net,
	hawk@...nel.org,
	john.fastabend@...il.com,
	bpf@...r.kernel.org,
	Song Yoong Siang <yoong.siang.song@...el.com>,
	Florian Bezdeka <florian.bezdeka@...mens.com>,
	Mor Bar-Gabay <morx.bar.gabay@...el.com>
Subject: [PATCH net 2/5] igc: Fix TX drops in XDP ZC

From: Zdenek Bouska <zdenek.bouska@...mens.com>

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>
Reviewed-by: Song Yoong Siang <yoong.siang.song@...el.com>
Reviewed-by: Florian Bezdeka <florian.bezdeka@...mens.com>
Tested-by: Mor Bar-Gabay <morx.bar.gabay@...el.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@...el.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 27c99ff59ed4..156d123c0e21 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;
-- 
2.47.1