netdev - Re: [PATCH bpf-next v2 3/4] ice: xsk: improve AF

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Date:   Thu, 30 Dec 2021 17:07:55 +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 v2 3/4] ice: xsk: improve AF_XDP ZC Tx and use batching API

From: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Date: Thu, 30 Dec 2021 14:13:10 +0100

> On Wed, Dec 29, 2021 at 02:11:31PM +0100, Alexander Lobakin wrote:
> > From: Maciej Fijalkowski <maciej.fijalkowski@...el.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@...el.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.

Ah okay, I confused it with a work around this pragma here: [0]

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

I think there are more potential call sites for that to come, I'd
make linux/unroll.h in the future I guess. But not as a part of
this series, right.

> 
> > 
> > 	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

[0] https://elixir.bootlin.com/linux/v5.16-rc7/source/arch/mips/include/asm/unroll.h#L16

Al