netdev - Re: [PATCH bpf-next v4 2/8] ice: xsk: force rings to be sized to power of 2

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Date:   Tue, 25 Jan 2022 12:23:06 +0100
From:   Alexander Lobakin <alexandr.lobakin@...el.com>
To:     Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Cc:     Alexander Lobakin <alexandr.lobakin@...el.com>,
        bpf@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        netdev@...r.kernel.org, magnus.karlsson@...el.com
Subject: Re: [PATCH bpf-next v4 2/8] ice: xsk: force rings to be sized to power of 2

From: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Date: Mon, 24 Jan 2022 17:55:41 +0100

> With the upcoming introduction of batching to XSK data path,
> performance wise it will be the best to have the ring descriptor count
> to be aligned to power of 2.
> 
> Check if rings sizes that user is going to attach the XSK socket fulfill
> the condition above. For Tx side, although check is being done against
> the Tx queue and in the end the socket will be attached to the XDP
> queue, it is fine since XDP queues get the ring->count setting from Tx
> queues.
> 
> Suggested-by: Alexander Lobakin <alexandr.lobakin@...el.com>
> Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
> ---
>  drivers/net/ethernet/intel/ice/ice_xsk.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/net/ethernet/intel/ice/ice_xsk.c b/drivers/net/ethernet/intel/ice/ice_xsk.c
> index 2388837d6d6c..0350f9c22c62 100644
> --- a/drivers/net/ethernet/intel/ice/ice_xsk.c
> +++ b/drivers/net/ethernet/intel/ice/ice_xsk.c
> @@ -327,6 +327,14 @@ int ice_xsk_pool_setup(struct ice_vsi *vsi, struct xsk_buff_pool *pool, u16 qid)
>  	bool if_running, pool_present = !!pool;
>  	int ret = 0, pool_failure = 0;
>  
> +	if (!is_power_of_2(vsi->rx_rings[qid]->count) ||
> +	    !is_power_of_2(vsi->tx_rings[qid]->count)) {
> +		netdev_err(vsi->netdev,
> +			   "Please align ring sizes at idx %d to power of 2\n", qid);

Ideally I'd pass xdp->extack from ice_xdp() to print this message
directly in userspace (note that NL_SET_ERR_MSG{,_MOD}() don't
support string formatting, but the user already knows QID at this
point).

> +		pool_failure = -EINVAL;
> +		goto failure;
> +	}
> +
>  	if_running = netif_running(vsi->netdev) && ice_is_xdp_ena_vsi(vsi);
>  
>  	if (if_running) {
> @@ -349,6 +357,7 @@ int ice_xsk_pool_setup(struct ice_vsi *vsi, struct xsk_buff_pool *pool, u16 qid)
>  			netdev_err(vsi->netdev, "ice_qp_ena error = %d\n", ret);
>  	}
>  
> +failure:
>  	if (pool_failure) {
>  		netdev_err(vsi->netdev, "Could not %sable buffer pool, error = %d\n",
>  			   pool_present ? "en" : "dis", pool_failure);
> -- 
> 2.33.1

Thanks,
Al