Subject: Re: [PATCH bpf-next v8 08/18] ice: Support XDP hints in AF_XDP ZC mode

From: Maciej Fijalkowski <[email-masked]>
Date: Tue, 12 Dec 2023 14:20:48 +0100

On Tue, Dec 05, 2023 at 10:08:37PM +0100, Larysa Zaremba wrote:
> In AF_XDP ZC, xdp_buff is not stored on ring,
> instead it is provided by xsk_buff_pool.
> Space for metadata sources right after such buffers was already reserved
> in commit 94ecc5ca4dbf ("xsk: Add cb area to struct xdp_buff_xsk").
> 
> Some things (such as pointer to packet context) do not change on a
> per-packet basis, so they can be set at the same time as RX queue info.
> On the other hand, RX descriptor is unique for each packet, but is already
> known when setting DMA addresses. This minimizes performance impact of
> hints on regular packet processing.
> 
> Update AF_XDP ZC packet processing to support XDP hints.
> 
> Co-developed-by: Maciej Fijalkowski <[email-masked]>
> Signed-off-by: Maciej Fijalkowski <[email-masked]>
> Signed-off-by: Larysa Zaremba <[email-masked]>

Not sure if I am supposed/allowed to provide review here, but:

Reviewed-by: Maciej Fijalkowski <[email-masked]>

LGTM

> ---
>  drivers/net/ethernet/intel/ice/ice_base.c | 14 ++++++++++++++
>  drivers/net/ethernet/intel/ice/ice_xsk.c  |  5 +++++
>  2 files changed, 19 insertions(+)
> 
> diff --git a/drivers/net/ethernet/intel/ice/ice_base.c b/drivers/net/ethernet/intel/ice/ice_base.c
> index 2d83f3c029e7..a040f02a342e 100644
> --- a/drivers/net/ethernet/intel/ice/ice_base.c
> +++ b/drivers/net/ethernet/intel/ice/ice_base.c
> @@ -519,6 +519,19 @@ static int ice_setup_rx_ctx(struct ice_rx_ring *ring)
>  	return 0;
>  }
>  
> +static void ice_xsk_pool_fill_cb(struct ice_rx_ring *ring)
> +{
> +	void *ctx_ptr = &ring->pkt_ctx;
> +	struct xsk_cb_desc desc = {};
> +
> +	XSK_CHECK_PRIV_TYPE(struct ice_xdp_buff);
> +	desc.src = &ctx_ptr;
> +	desc.off = offsetof(struct ice_xdp_buff, pkt_ctx) -
> +		   sizeof(struct xdp_buff);
> +	desc.bytes = sizeof(ctx_ptr);
> +	xsk_pool_fill_cb(ring->xsk_pool, &desc);
> +}
> +
>  /**
>   * ice_vsi_cfg_rxq - Configure an Rx queue
>   * @ring: the ring being configured
> @@ -553,6 +566,7 @@ int ice_vsi_cfg_rxq(struct ice_rx_ring *ring)
>  			if (err)
>  				return err;
>  			xsk_pool_set_rxq_info(ring->xsk_pool, &ring->xdp_rxq);
> +			ice_xsk_pool_fill_cb(ring);
>  
>  			dev_info(dev, "Registered XDP mem model MEM_TYPE_XSK_BUFF_POOL on Rx ring %d\n",
>  				 ring->q_index);
> diff --git a/drivers/net/ethernet/intel/ice/ice_xsk.c b/drivers/net/ethernet/intel/ice/ice_xsk.c
> index 906e383e864a..11b6114ab83d 100644
> --- a/drivers/net/ethernet/intel/ice/ice_xsk.c
> +++ b/drivers/net/ethernet/intel/ice/ice_xsk.c
> @@ -458,6 +458,11 @@ static u16 ice_fill_rx_descs(struct xsk_buff_pool *pool, struct xdp_buff **xdp,
>  		rx_desc->read.pkt_addr = cpu_to_le64(dma);
>  		rx_desc->wb.status_error0 = 0;
>  
> +		/* Put private info that changes on a per-packet basis
> +		 * into xdp_buff_xsk->cb.
> +		 */
> +		ice_xdp_meta_set_desc(*xdp, rx_desc);
> +
>  		rx_desc++;
>  		xdp++;
>  	}
> -- 
> 2.41.0
>