netdev - Re: [Intel-wired-lan] [PATCH v3 iwl-net 1/8] ice: respect netif readiness in AF

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Date: Tue, 11 Jun 2024 13:59:37 +0200
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
CC: <intel-wired-lan@...ts.osuosl.org>, <larysa.zaremba@...el.com>,
	<netdev@...r.kernel.org>, <michal.kubiak@...el.com>,
	<anthony.l.nguyen@...el.com>, <jacob.e.keller@...el.com>, Chandan Kumar Rout
	<chandanx.rout@...el.com>, <magnus.karlsson@...el.com>, Shannon Nelson
	<shannon.nelson@....com>
Subject: Re: [Intel-wired-lan] [PATCH v3 iwl-net 1/8] ice: respect netif
 readiness in AF_XDP ZC related ndo's

From: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Date: Tue,  4 Jun 2024 15:21:48 +0200

> From: Michal Kubiak <michal.kubiak@...el.com>
> 
> Address a scenario in which XSK ZC Tx produces descriptors to XDP Tx
> ring when link is either not yet fully initialized or process of
> stopping the netdev has already started. To avoid this, add checks
> against carrier readiness in ice_xsk_wakeup() and in ice_xmit_zc().
> One could argue that bailing out early in ice_xsk_wakeup() would be
> sufficient but given the fact that we produce Tx descriptors on behalf
> of NAPI that is triggered for Rx traffic, the latter is also needed.
> 
> Bringing link up is an asynchronous event executed within
> ice_service_task so even though interface has been brought up there is
> still a time frame where link is not yet ok.
> 
> Without this patch, when AF_XDP ZC Tx is used simultaneously with stack
> Tx, Tx timeouts occur after going through link flap (admin brings
> interface down then up again). HW seem to be unable to transmit
> descriptor to the wire after HW tail register bump which in turn causes
> bit __QUEUE_STATE_STACK_XOFF to be set forever as
> netdev_tx_completed_queue() sees no cleaned bytes on the input.
> 
> Fixes: 126cdfe1007a ("ice: xsk: Improve AF_XDP ZC Tx and use batching API")
> Fixes: 2d4238f55697 ("ice: Add support for AF_XDP")
> Reviewed-by: Shannon Nelson <shannon.nelson@....com>
> Tested-by: Chandan Kumar Rout <chandanx.rout@...el.com> (A Contingent Worker at Intel)
> Signed-off-by: Michal Kubiak <michal.kubiak@...el.com>
> Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
> ---
>  drivers/net/ethernet/intel/ice/ice_xsk.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/intel/ice/ice_xsk.c b/drivers/net/ethernet/intel/ice/ice_xsk.c
> index 2015f66b0cf9..1bd4b054dd80 100644
> --- a/drivers/net/ethernet/intel/ice/ice_xsk.c
> +++ b/drivers/net/ethernet/intel/ice/ice_xsk.c
> @@ -1048,6 +1048,10 @@ bool ice_xmit_zc(struct ice_tx_ring *xdp_ring)
>  
>  	ice_clean_xdp_irq_zc(xdp_ring);
>  
> +	if (!netif_carrier_ok(xdp_ring->vsi->netdev) ||
> +	    !netif_running(xdp_ring->vsi->netdev))
> +		return true;

Why is it checked after clean_xdp_irq_zc()?
Also, unlikely()?

> +
>  	budget = ICE_DESC_UNUSED(xdp_ring);
>  	budget = min_t(u16, budget, ICE_RING_QUARTER(xdp_ring));
>  
> @@ -1091,7 +1095,7 @@ ice_xsk_wakeup(struct net_device *netdev, u32 queue_id,
>  	struct ice_vsi *vsi = np->vsi;
>  	struct ice_tx_ring *ring;
>  
> -	if (test_bit(ICE_VSI_DOWN, vsi->state))
> +	if (test_bit(ICE_VSI_DOWN, vsi->state) || !netif_carrier_ok(netdev))

Same for unlikely()?

>  		return -ENETDOWN;
>  
>  	if (!ice_is_xdp_ena_vsi(vsi))

Thanks,
Olek