netdev - Re: [PATCH net 2/2] tsnep: Fix XDP_RING_NEED

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Date: Thu, 25 Jan 2024 12:06:28 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Gerhard Engleder <gerhard@...leder-embedded.com>,
 netdev@...r.kernel.org,  bpf@...r.kernel.org
Cc: davem@...emloft.net, kuba@...nel.org, edumazet@...gle.com,
 bjorn@...nel.org,  magnus.karlsson@...el.com, maciej.fijalkowski@...el.com,
  jonathan.lemon@...il.com
Subject: Re: [PATCH net 2/2] tsnep: Fix XDP_RING_NEED_WAKEUP for empty fill
 ring

On Tue, 2024-01-23 at 21:09 +0100, Gerhard Engleder wrote:
> The fill ring of the XDP socket may contain not enough buffers to
> completey fill the RX queue during socket creation. In this case the
> flag XDP_RING_NEED_WAKEUP is not set as this flag is only set if the RX
> queue is not completely filled during polling.
> 
> Set XDP_RING_NEED_WAKEUP flag also if RX queue is not completely filled
> during XDP socket creation.
> 
> Fixes: 3fc2333933fd ("tsnep: Add XDP socket zero-copy RX support")
> Signed-off-by: Gerhard Engleder <gerhard@...leder-embedded.com>
> ---
>  drivers/net/ethernet/engleder/tsnep_main.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/net/ethernet/engleder/tsnep_main.c b/drivers/net/ethernet/engleder/tsnep_main.c
> index d380a407e175..ae0b8b37b9bf 100644
> --- a/drivers/net/ethernet/engleder/tsnep_main.c
> +++ b/drivers/net/ethernet/engleder/tsnep_main.c
> @@ -1764,6 +1764,19 @@ static void tsnep_rx_reopen_xsk(struct tsnep_rx *rx)
>  			allocated--;
>  		}
>  	}
> +
> +	/* set need wakeup flag immediately if ring is not filled completely,
> +	 * first polling would be too late as need wakeup signalisation would
> +	 * be delayed for an indefinite time
> +	 */
> +	if (xsk_uses_need_wakeup(rx->xsk_pool)) {
> +		int desc_available = tsnep_rx_desc_available(rx);
> +
> +		if (desc_available)
> +			xsk_set_rx_need_wakeup(rx->xsk_pool);
> +		else
> +			xsk_clear_rx_need_wakeup(rx->xsk_pool);
> +	}
>  }
>  
>  static bool tsnep_pending(struct tsnep_queue *queue)

The patch LGTM, but there is a very similar chunk of code in
tsnep_rx_poll_zc(). You should consider a net-next follow-up
consolidating the code in a common helper.

Cheers,

Paolo