Subject: Re: [PATCH 2/2] Trigger proper interrupts in igc_xsk_wakeup

From: Vinicius Costa Gomes <[email-masked]>
Date: Mon, 18 Apr 2022 13:44:35 -0400

Jeff Evanson <[email-masked]> writes:

> in igc_xsk_wakeup, trigger the proper interrupt based on whether flags
> contains XDP_WAKEUP_RX and/or XDP_WAKEUP_TX
>
> Signed-off-by: Jeff Evanson <[email-masked]>
> ---
>  drivers/net/ethernet/intel/igc/igc_main.c | 36 +++++++++++++++++------
>  1 file changed, 27 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
> index a36a18c84aeb..d706de95dc06 100644
> --- a/drivers/net/ethernet/intel/igc/igc_main.c
> +++ b/drivers/net/ethernet/intel/igc/igc_main.c
> @@ -6073,7 +6073,7 @@ static void igc_trigger_rxtxq_interrupt(struct igc_adapter *adapter,
>  int igc_xsk_wakeup(struct net_device *dev, u32 queue_id, u32 flags)
>  {
>  	struct igc_adapter *adapter = netdev_priv(dev);
> -	struct igc_q_vector *q_vector;
> +	struct igc_q_vector *txq_vector = 0, *rxq_vector = 0;
>  	struct igc_ring *ring;
>  
>  	if (test_bit(__IGC_DOWN, &adapter->state))
> @@ -6082,17 +6082,35 @@ int igc_xsk_wakeup(struct net_device *dev, u32 queue_id, u32 flags)
>  	if (!igc_xdp_is_enabled(adapter))
>  		return -ENXIO;
>  
> -	if (queue_id >= adapter->num_rx_queues)
> -		return -EINVAL;
> +	if (flags & XDP_WAKEUP_RX) {
> +		if (queue_id >= adapter->num_rx_queues)
> +			return -EINVAL;
>  
> -	ring = adapter->rx_ring[queue_id];
> +		ring = adapter->rx_ring[queue_id];
> +		if (!ring->xsk_pool)
> +			return -ENXIO;
>  
> -	if (!ring->xsk_pool)
> -		return -ENXIO;
> +		rxq_vector = ring->q_vector;
> +	}
> +
> +	if (flags & XDP_WAKEUP_TX) {
> +		if (queue_id >= adapter->num_tx_queues)
> +			return -EINVAL;
> +
> +		ring = adapter->tx_ring[queue_id];
> +		if (!ring->xsk_pool)
> +			return -ENXIO;
> +
> +		txq_vector = ring->q_vector;
> +	}
> +
> +	if (rxq_vector &&
> +	    !napi_if_scheduled_mark_missed(&rxq_vector->napi))
> +		igc_trigger_rxtxq_interrupt(adapter, rxq_vector);
>  
> -	q_vector = adapter->q_vector[queue_id];
> -	if (!napi_if_scheduled_mark_missed(&q_vector->napi))
> -		igc_trigger_rxtxq_interrupt(adapter, q_vector);
> +	if (txq_vector && txq_vector != rxq_vector &&
> +	    !napi_if_scheduled_mark_missed(&txq_vector->napi))
> +		igc_trigger_rxtxq_interrupt(adapter, txq_vector);

Two things:
 - My imagination was not able to produce a scenario where this commit
 would solve any problems. Can you explain better the case where the
 current code would cause the wrong interrupt to be generated (or miss
 generating an interrupt)? (this should be in the commit message)
 - I think that with this patch applied, there would cases (both TX and
 RX flags set) that we cause two writes into the EICS register. That
 could cause unnecessary wakeups.

>  	return 0;
>  }
> -- 
> 2.17.1

Cheers,
-- 
Vinicius