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

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Message-ID: <d4b15c726e7c2219eb09b094ae9fc1299fae51e8.camel@siemens.com>
Date: Wed, 19 Mar 2025 17:16:35 +0100
From: Florian Bezdeka <florian.bezdeka@...mens.com>
To: Zdenek Bouska <zdenek.bouska@...mens.com>, 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>
Cc: intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH net-next] igc: Fix TX drops in XDP ZC

On Wed, 2025-03-19 at 15:18 +0100, Zdenek Bouska 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: Florian Bezdeka <florian.bezdeka@...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