xdp: introduce bulking for page_pool tx return path

XDP bulk APIs introduce a defer/flush mechanism to return pages belonging to the same xdp_mem_allocator object (identified via the mem.id field) in bulk to optimize I-cache and D-cache since xdp_return_frame is usually run inside the driver NAPI tx completion loop.
Convert mvneta, mvpp2 and mlx5 drivers to xdp_return_frame_bulk APIs.

More details on benchmarks run on mlx5 can be found here:
https://github.com/xdp-project/xdp-project/blob/master/areas/mem/xdp_bulk_return01.org

Changes since v5:
- do not keep looping over ptr_ring if the cache is full but release leftover pages running page_pool_return_page

Changes since v4:
- fix comments
- introduce xdp_frame_bulk_init utility routine
- compiler annotations for I-cache code layout
- move rcu_read_lock outside fast-path
- mlx5 xdp bulking code optimization

Changes since v3:
- align DEV_MAP_BULK_SIZE to XDP_BULK_QUEUE_SIZE
- refactor page_pool_put_page_bulk to avoid code duplication

Changes since v2:
- move mvneta changes in a dedicated patch

Changes since v1:
- improve comments
- rework xdp_return_frame_bulk routine logic
- move count and xa fields at the beginning of xdp_frame_bulk struct
- invert logic in page_pool_put_page_bulk for loop

Lorenzo Bianconi (5):
net: xdp: introduce bulking for xdp tx return path
net: page_pool: add bulk support for ptr_ring
net: mvneta: add xdp tx return bulking support
net: mvpp2: add xdp tx return bulking support
net: mlx5: add xdp tx return bulking support

 drivers/net/ethernet/marvell/mvneta.c         | 10 ++-
 .../net/ethernet/marvell/mvpp2/mvpp2_main.c   | 10 ++-
 .../net/ethernet/mellanox/mlx5/core/en/xdp.c  | 22 ++++--
 include/net/page_pool.h                       | 26 +++++++
 include/net/xdp.h                             | 17 ++++-
 net/core/page_pool.c                          | 70 ++++++++++++++++---
 net/core/xdp.c                                | 54 ++++++++++++++
 7 files changed, 192 insertions(+), 17 deletions(-)

2.26.2