Subject: Re: [PATCH net-next 6/9] ionic: Add XDP_TX support

From: Jakub Kicinski <[email-masked]>
Date: Wed, 31 Jan 2024 18:25:05 -0800

On Mon, 29 Jan 2024 17:30:39 -0800 Shannon Nelson wrote:
>  	case XDP_TX:
> +		xdpf = xdp_convert_buff_to_frame(&xdp_buf);
> +		if (!xdpf)
> +			goto out_xdp_abort;
> +
> +		txq = rxq->partner;
> +		nq = netdev_get_tx_queue(netdev, txq->index);
> +		__netif_tx_lock(nq, smp_processor_id());
> +
> +		if (netif_tx_queue_stopped(nq) ||
> +		    unlikely(ionic_maybe_stop_tx(txq, 1))) {
> +			__netif_tx_unlock(nq);
> +			goto out_xdp_abort;
> +		}
> +
> +		dma_unmap_page(rxq->dev, buf_info->dma_addr,
> +			       IONIC_PAGE_SIZE, DMA_FROM_DEVICE);
> +
> +		err = ionic_xdp_post_frame(netdev, txq, xdpf, XDP_TX,
> +					   buf_info->page,
> +					   buf_info->page_offset,
> +					   true);

I think that you need txq_trans_cond_update() somewhere, otherwise 
if XDP starves stack Tx the stack will think the queue is stalled.

> +		__netif_tx_unlock(nq);
> +		if (err) {
> +			netdev_dbg(netdev, "tx ionic_xdp_post_frame err %d\n", err);
> +			goto out_xdp_abort;
> +		}
> +		stats->xdp_tx++;
> +
> +		/* the Tx completion will free the buffers */
> +		break;
> +
>  	case XDP_ABORTED:
>  	default:
> -		trace_xdp_exception(netdev, xdp_prog, xdp_action);
> -		ionic_rx_page_free(rxq, buf_info);
> -		stats->xdp_aborted++;
> +		goto out_xdp_abort;
>  	}
>  
> +	return true;
> +
> +out_xdp_abort:
> +	trace_xdp_exception(netdev, xdp_prog, xdp_action);
> +	ionic_rx_page_free(rxq, buf_info);
> +	stats->xdp_aborted++;
> +
>  	return true;
>  }
>  
> @@ -880,6 +1001,16 @@ static void ionic_tx_clean(struct ionic_queue *q,
>  	struct sk_buff *skb = cb_arg;
>  	u16 qi;
>  
> +	if (desc_info->xdpf) {
> +		ionic_xdp_tx_desc_clean(q->partner, desc_info);
> +		stats->clean++;
> +
> +		if (unlikely(__netif_subqueue_stopped(q->lif->netdev, q->index)))
> +			netif_wake_subqueue(q->lif->netdev, q->index);
> +
> +		return;
> +	}

You can't complete XDP if NAPI budget is 0, you may be in hard IRQ
context if its netpoll calling :(