Re: [PATCH bpf-next v2 3/4] ice: xsk: improve AF_XDP ZC Tx and use batching API

[Maciej Fijalkowski <maciej.fijalkowski@intel.com>]

On Wed, Dec 29, 2021 at 02:11:31PM +0100, Alexander Lobakin wrote:
> From: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
> Date: Thu, 16 Dec 2021 14:59:57 +0100
> 
> > Follow mostly the logic from commit 9610bd988df9 ("ice: optimize XDP_TX
> > workloads") that has been done in order to address the massive tx_busy
> > statistic bump and improve the performance as well.
> > 
> > Increase the ICE_TX_THRESH to 64 as it seems to work out better for both
> > XDP and AF_XDP. Also, separating the stats structs onto separate cache
> > lines seemed to improve the performance. Batching approach is inspired
> > by i40e's implementation with adjustments to the cleaning logic.
> > 
> > One difference from 'xdpdrv' XDP_TX is when ring has less than
> > ICE_TX_THRESH free entries, the cleaning routine will not stop after
> > cleaning a single ICE_TX_THRESH amount of descs but rather will forward
> > the next_dd pointer and check the DD bit and for this bit being set the
> > cleaning will be repeated. IOW clean until there are descs that can be
> > cleaned.
> > 
> > It takes three separate xdpsock instances in txonly mode to achieve the
> > line rate and this was not previously possible.
> > 
> > Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
> > ---
> >  drivers/net/ethernet/intel/ice/ice_txrx.c |   2 +-
> >  drivers/net/ethernet/intel/ice/ice_txrx.h |   4 +-
> >  drivers/net/ethernet/intel/ice/ice_xsk.c  | 249 ++++++++++++++--------
> >  drivers/net/ethernet/intel/ice/ice_xsk.h  |  26 ++-
> >  4 files changed, 182 insertions(+), 99 deletions(-)
> > 
> 
> -- 8< --
> 
> > diff --git a/drivers/net/ethernet/intel/ice/ice_xsk.h b/drivers/net/ethernet/intel/ice/ice_xsk.h
> > index 4c7bd8e9dfc4..f2eb99063c1f 100644
> > --- a/drivers/net/ethernet/intel/ice/ice_xsk.h
> > +++ b/drivers/net/ethernet/intel/ice/ice_xsk.h
> > @@ -6,19 +6,36 @@
> >  #include "ice_txrx.h"
> >  #include "ice.h"
> >  
> > +#define PKTS_PER_BATCH 8
> > +
> > +#ifdef __clang__
> > +#define loop_unrolled_for _Pragma("clang loop unroll_count(8)") for
> > +#elif __GNUC__ >= 4
> > +#define loop_unrolled_for _Pragma("GCC unroll 8") for
> > +#else
> > +#define loop_unrolled_for for
> > +#endif
> 
> It's used in a bunch more places across the tree, what about
> defining that in linux/compiler{,_clang,_gcc}.h?
> Is it possible to pass '8' as an argument? Like

Like where besides i40e? I might currently suck at grepping, let's blame
christmas break for that.

If there are actually other callsites besides i40e then this is a good
idea to me, maybe as a follow-up?

> 
> 	loop_unrolled_for(PKTS_PER_BATCH) ( ; ; ) { }
> 
> Could be quite handy.
> If it is not, I'd maybe try to define a couple of precoded macros
> for 8, 16 and 32, like
> 
> #define loop_unrolled_for_8 ...
> #define loop_unrolled_for_16 ...
> ...
> 
> So they could be used as generic. I don't think I've seen them with
> values other than 8-32.
> 
> > +
> >  struct ice_vsi;
> >  
> >  #ifdef CONFIG_XDP_SOCKETS
> >  int ice_xsk_pool_setup(struct ice_vsi *vsi, struct xsk_buff_pool *pool,
> >  		       u16 qid);
> >  int ice_clean_rx_irq_zc(struct ice_rx_ring *rx_ring, int budget);
> > -bool ice_clean_tx_irq_zc(struct ice_tx_ring *xdp_ring, int budget);
> >  int ice_xsk_wakeup(struct net_device *netdev, u32 queue_id, u32 flags);
> >  bool ice_alloc_rx_bufs_zc(struct ice_rx_ring *rx_ring, u16 count);
> >  bool ice_xsk_any_rx_ring_ena(struct ice_vsi *vsi);
> >  void ice_xsk_clean_rx_ring(struct ice_rx_ring *rx_ring);
> >  void ice_xsk_clean_xdp_ring(struct ice_tx_ring *xdp_ring);
> > +bool ice_xmit_zc(struct ice_tx_ring *xdp_ring, u32 budget);
> >  #else
> > +static inline bool
> > +ice_xmit_zc(struct ice_tx_ring __always_unused *xdp_ring,
> > +	    u32 __always_unused budget)
> > +{
> > +	return false;
> > +}
> > +
> >  static inline int
> >  ice_xsk_pool_setup(struct ice_vsi __always_unused *vsi,
> >  		   struct xsk_buff_pool __always_unused *pool,
> > @@ -34,13 +51,6 @@ ice_clean_rx_irq_zc(struct ice_rx_ring __always_unused *rx_ring,
> >  	return 0;
> >  }
> >  
> > -static inline bool
> > -ice_clean_tx_irq_zc(struct ice_tx_ring __always_unused *xdp_ring,
> > -		    int __always_unused budget)
> > -{
> > -	return false;
> > -}
> > -
> >  static inline bool
> >  ice_alloc_rx_bufs_zc(struct ice_rx_ring __always_unused *rx_ring,
> >  		     u16 __always_unused count)
> > -- 
> > 2.33.1
> 
> Thanks,
> Al