netdev - Re: [PATCH bpf-next v4 3/8] i40e: add support for AF_XDP need

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Date:   Wed, 14 Aug 2019 07:48:28 -0700
From:   "Jonathan Lemon" <jonathan.lemon@...il.com>
To:     "Magnus Karlsson" <magnus.karlsson@...el.com>
Cc:     bjorn.topel@...el.com, ast@...nel.org, daniel@...earbox.net,
        netdev@...r.kernel.org, brouer@...hat.com, maximmi@...lanox.com,
        bpf@...r.kernel.org, bruce.richardson@...el.com,
        ciara.loftus@...el.com, jakub.kicinski@...ronome.com,
        xiaolong.ye@...el.com, qi.z.zhang@...el.com,
        sridhar.samudrala@...el.com, kevin.laatz@...el.com,
        ilias.apalodimas@...aro.org, kiran.patil@...el.com,
        axboe@...nel.dk, maciej.fijalkowski@...el.com,
        maciejromanfijalkowski@...il.com, intel-wired-lan@...ts.osuosl.org
Subject: Re: [PATCH bpf-next v4 3/8] i40e: add support for AF_XDP need_wakeup
 feature



On 14 Aug 2019, at 0:27, Magnus Karlsson wrote:

> This patch adds support for the need_wakeup feature of AF_XDP. If the
> application has told the kernel that it might sleep using the new bind
> flag XDP_USE_NEED_WAKEUP, the driver will then set this flag if it has
> no more buffers on the NIC Rx ring and yield to the application. For
> Tx, it will set the flag if it has no outstanding Tx completion
> interrupts and return to the application.
>
> Signed-off-by: Magnus Karlsson <magnus.karlsson@...el.com>
> ---
>  drivers/net/ethernet/intel/i40e/i40e_xsk.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
>
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_xsk.c 
> b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> index d0ff5d8..42c9012 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> @@ -626,6 +626,15 @@ int i40e_clean_rx_irq_zc(struct i40e_ring 
> *rx_ring, int budget)
>
>  	i40e_finalize_xdp_rx(rx_ring, xdp_xmit);
>  	i40e_update_rx_stats(rx_ring, total_rx_bytes, total_rx_packets);
> +
> +	if (xsk_umem_uses_need_wakeup(rx_ring->xsk_umem)) {
> +		if (failure || rx_ring->next_to_clean == rx_ring->next_to_use)
> +			xsk_set_rx_need_wakeup(rx_ring->xsk_umem);
> +		else
> +			xsk_clear_rx_need_wakeup(rx_ring->xsk_umem);
> +
> +		return (int)total_rx_packets;
> +	}
>  	return failure ? budget : (int)total_rx_packets;

Can you elaborate why we're not returning the total budget on failure
for the wakeup case?