Subject: Re: [PATCH bpf-next v7 08/18] ice: Support XDP hints in AF_XDP ZC mode

From: Maciej Fijalkowski <[email-masked]>
Date: Thu, 16 Nov 2023 13:49:36 +0100

On Wed, Nov 15, 2023 at 06:52:50PM +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]>
> ---
>  drivers/net/ethernet/intel/ice/ice_base.c | 13 +++++++++++++
>  drivers/net/ethernet/intel/ice/ice_xsk.c  | 17 +++++++++++------
>  2 files changed, 24 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ice/ice_base.c b/drivers/net/ethernet/intel/ice/ice_base.c
> index 2d83f3c029e7..d3396c1c87a9 100644
> --- a/drivers/net/ethernet/intel/ice/ice_base.c
> +++ b/drivers/net/ethernet/intel/ice/ice_base.c
> @@ -519,6 +519,18 @@ 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 = {};
> +
> +	desc.src = &ctx_ptr;
> +	desc.off = offsetof(struct ice_xdp_buff, pkt_ctx) -
> +		   sizeof(struct xdp_buff);

Took me a while to figure out this offset calculation:D

> +	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 +565,7 @@ 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);

A good place for XSK_CHECK_PRIV_TYPE() ?

> +			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..a690e34ea8ae 100644
> --- a/drivers/net/ethernet/intel/ice/ice_xsk.c
> +++ b/drivers/net/ethernet/intel/ice/ice_xsk.c
> @@ -433,7 +433,7 @@ int ice_xsk_pool_setup(struct ice_vsi *vsi, struct xsk_buff_pool *pool, u16 qid)
>  
>  /**
>   * ice_fill_rx_descs - pick buffers from XSK buffer pool and use it
> - * @pool: XSK Buffer pool to pull the buffers from
> + * @rx_ring: rx ring
>   * @xdp: SW ring of xdp_buff that will hold the buffers
>   * @rx_desc: Pointer to Rx descriptors that will be filled
>   * @count: The number of buffers to allocate
> @@ -445,19 +445,24 @@ int ice_xsk_pool_setup(struct ice_vsi *vsi, struct xsk_buff_pool *pool, u16 qid)
>   *
>   * Returns the amount of allocated Rx descriptors
>   */
> -static u16 ice_fill_rx_descs(struct xsk_buff_pool *pool, struct xdp_buff **xdp,
> +static u16 ice_fill_rx_descs(struct ice_rx_ring *rx_ring, struct xdp_buff **xdp,

Might be lack of caffeine on my side, but I don't see a reason for passing
rx_ring down to ice_fill_rx_descs() ?

I see I introduced this in the code example previously but it must have
been some leftover from previous hacking...

Help!

>  			     union ice_32b_rx_flex_desc *rx_desc, u16 count)
>  {
>  	dma_addr_t dma;
>  	u16 buffs;
>  	int i;
>  
> -	buffs = xsk_buff_alloc_batch(pool, xdp, count);
> +	buffs = xsk_buff_alloc_batch(rx_ring->xsk_pool, xdp, count);
>  	for (i = 0; i < buffs; i++) {
>  		dma = xsk_buff_xdp_get_dma(*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++;
>  	}
> @@ -488,8 +493,7 @@ static bool __ice_alloc_rx_bufs_zc(struct ice_rx_ring *rx_ring, u16 count)
>  	xdp = ice_xdp_buf(rx_ring, ntu);
>  
>  	if (ntu + count >= rx_ring->count) {
> -		nb_buffs_extra = ice_fill_rx_descs(rx_ring->xsk_pool, xdp,
> -						   rx_desc,
> +		nb_buffs_extra = ice_fill_rx_descs(rx_ring, xdp, rx_desc,
>  						   rx_ring->count - ntu);
>  		if (nb_buffs_extra != rx_ring->count - ntu) {
>  			ntu += nb_buffs_extra;
> @@ -502,7 +506,7 @@ static bool __ice_alloc_rx_bufs_zc(struct ice_rx_ring *rx_ring, u16 count)
>  		ice_release_rx_desc(rx_ring, 0);
>  	}
>  
> -	nb_buffs = ice_fill_rx_descs(rx_ring->xsk_pool, xdp, rx_desc, count);
> +	nb_buffs = ice_fill_rx_descs(rx_ring, xdp, rx_desc, count);
>  
>  	ntu += nb_buffs;
>  	if (ntu == rx_ring->count)
> @@ -752,6 +756,7 @@ static int ice_xmit_xdp_tx_zc(struct xdp_buff *xdp,
>   * @xdp: xdp_buff used as input to the XDP program
>   * @xdp_prog: XDP program to run
>   * @xdp_ring: ring to be used for XDP_TX action
> + * @rx_desc: packet descriptor

leftover comment from previous approach

>   *
>   * Returns any of ICE_XDP_{PASS, CONSUMED, TX, REDIR}
>   */
> -- 
> 2.41.0
>