RE: [Intel-wired-lan] [PATCH intel-net 2/2] ice: xsk: use Rx ring's XDP ring when picking NAPI context

> -----Original Message-----
> From: Intel-wired-lan <[email protected]> On Behalf Of Maciej
> Fijalkowski
> Sent: Thursday, August 11, 2022 11:52 PM
> To: [email protected]
> Cc: [email protected]; [email protected]; Karlsson,
> Magnus <[email protected]>
> Subject: [Intel-wired-lan] [PATCH intel-net 2/2] ice: xsk: use Rx ring's XDP ring
> when picking NAPI context
> 
> Ice driver allocates per cpu XDP queues so that redirect path can safely use
> smp_processor_id() as an index to the array. At the same time though, XDP rings
> are used to pick NAPI context to call napi_schedule() or set
> NAPIF_STATE_MISSED. When user reduces queue count, say to 8, and
> num_possible_cpus() of underlying platform is 44, then this means queue vectors
> with correlated NAPI contexts will carry several XDP queues.
> 
> This in turn can result in a broken behavior where NAPI context of interest will
> never be scheduled and AF_XDP socket will not process any traffic.
> 
> To fix this, let us change the way how XDP rings are assigned to Rx rings and
> use this information later on when setting ice_tx_ring::xsk_pool pointer. For each
> Rx ring, grab the associated queue vector and walk through Tx ring's linked list.
> Once we stumble upon XDP ring in it, assign this ring to ice_rx_ring::xdp_ring.
> 
> Previous [0] approach of fixing this issue was for txonly scenario because of the
> described grouping of XDP rings across queue vectors. So, relying on Rx ring
> meant that NAPI context could be scheduled with a queue vector without XDP ring
> with associated XSK pool.
> 
> [0]: https://lore.kernel.org/netdev/20220707161128.54215-1-
> [email protected]/
> 
> Fixes: 2d4238f55697 ("ice: Add support for AF_XDP")
> Fixes: 22bf877e528f ("ice: introduce XDP_TX fallback path")
> Signed-off-by: Maciej Fijalkowski <[email protected]>
> ---
>  drivers/net/ethernet/intel/ice/ice.h      | 36 +++++++++++++++--------
>  drivers/net/ethernet/intel/ice/ice_lib.c  |  4 +--
> drivers/net/ethernet/intel/ice/ice_main.c | 25 +++++++++++-----
> drivers/net/ethernet/intel/ice/ice_xsk.c  | 12 ++++----
>  4 files changed, 48 insertions(+), 29 deletions(-)
> 

Tested-by: George Kuruvinakunnel <[email protected]>