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

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Message-ID: <PH0PR11MB5830C173F108E4B8F60C3611D8D92@PH0PR11MB5830.namprd11.prod.outlook.com>
Date: Wed, 19 Mar 2025 15:06:14 +0000
From: "Song, Yoong Siang" <yoong.siang.song@...el.com>
To: "Bouska, Zdenek" <zdenek.bouska@...mens.com>, "Nguyen, Anthony L"
	<anthony.l.nguyen@...el.com>, "Kitszel, Przemyslaw"
	<przemyslaw.kitszel@...el.com>, Andrew Lunn <andrew+netdev@...n.ch>, "David
 S. Miller" <davem@...emloft.net>, "Dumazet, Eric" <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>, "Fijalkowski, Maciej"
	<maciej.fijalkowski@...el.com>, "Joseph, Jithu" <jithu.joseph@...el.com>,
	"Bezdeka, Florian" <florian.bezdeka@...mens.com>
CC: "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"bpf@...r.kernel.org" <bpf@...r.kernel.org>, "Bouska, Zdenek"
	<zdenek.bouska@...mens.com>
Subject: RE: [PATCH net-next] igc: Fix TX drops in XDP ZC

On Wednesday, March 19, 2025 10:19 PM, Zdenek Bouska <zdenek.bouska@...mens.com> wrote:
>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>

>---
> 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