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

[Larysa Zaremba <larysa.zaremba@intel.com>]

On Thu, Nov 16, 2023 at 01:49:36PM +0100, Maciej Fijalkowski wrote:
> 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 <maciej.fijalkowski@intel.com>
> > Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
> > Signed-off-by: Larysa Zaremba <larysa.zaremba@intel.com>
> > ---
> >  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
>

Do you have a suggestion, how to make it easier to understand?
 
> > +	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() ?

Seems so, have not noticed that it was missing :(

> 
> > +			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!

It is lack of caffeine on both sides. I have missed the fact that indeed, we do 
not need rx_ring here.

> 
> >  			     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
> 

Will fix.

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