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

[Florian Bezdeka]

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@xxxxxxxxxxx>

Reviewed-by: Florian Bezdeka <florian.bezdeka@xxxxxxxxxxx>

> ---
>  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