[PATCH iwl-next v3 0/9] ice: properly use u64_stats API for all ring stats

[Jacob Keller <jacob.e.keller@intel.com>]

The ice driver has multiple u64 values stored in the ring structures for
each queue used for statistics. These are accumulated in
ice_update_vsi_stats(). The packet and byte values are read using the
u64_stats API from <linux/u64_stats_sync.h>.

Several non-standard counters are also accumulated in the same function,
but do not use the u64_stats API. This could result in load/store tears on
32-bit architectures. Further, since commit 316580b69d0a ("u64_stats:
provide u64_stats_t type"), the u64 stats API has had u64_stats_t and
access functions which convert to local64_t on 64-bit architectures.

The ice driver doesn't use u64_stats_t and these access functions. Thus
even on 64-bit architectures it could read inconsistent values. This series
refactors the ice driver to use the updated API. Along the way I noticed
several other issues and inconsistencies which I have cleaned up,
summarized below.

*) The driver never called u64_stats_init, leaving the syncp improperly
   initialized. Since the field is part of a kzalloc block, this only
   impacts 32-bit systems with CONFIG_LOCKDEP enabled.

*) A few locations accessed the packets and byte counts directly without
   using the u64 stats API.

*) The prev_pkt integer field is moved out of the stats structure and into
   the ice_tx_ring structure directly.

*) Cache line comments in ice_tx_ring and ice_rx_ring were out of date and
   did not match the actual intended layout for systems with 64-bit cache
   lines. Convert the structures to use __cacheline_group instead of
   comments.

*) The ice_fetch_u64_stats_per_ring() function took the ice_q_stats by
   value, defeating the point of using the u64_stats API entirely.

To keep the stats increments short, I introduced ice_stats_inc, as
otherwise each stat increment has to be quite verbose. Similarly a few
places read only one stat, so I added ice_stats_read for those.

This version uses struct ice_vsi_(tx|rx)_stats structures defined in
ice_main.c for the accumulator. I haven't come up with a better solution
that allows accumulating nicely without this structure. Its a bit
frustrating as it copies the entries in the ring stats structures but with
u64 instead of u64_stats_t.

I am also still not entirely certain how the ice_update_vsi_ring_stats()
function is synchronized in the ice driver. It is called from multiple
places without an obvious synchronization mechanism. It is ultimately
called from the service task and from ethtool, and I think it may also be
called from one of the netdev stats callbacks.

I'm open to suggestions on ways to improve this, as I think the result
still has some ugly logic and a fair amount of near duplicate code.

I have included the cacheline cleanup in ice_tx_ring and ice_rx_ring here,
but that could arguably be split to its own series. I only noticed it
because of attempting to move the prev_pkt field out of the ring stats. I
replaced the comments with cacheline_group, but I did not make an attempt
to optimize the existing cachelines. Probably we should experiment with the
method used in idpf with the 'read-mostly', 'read-write' and 'cold'
groupings, but doing so will require a more thorough deep dive on
performance profiling and tuning.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
---
Changes in v3:
- Use SMP_CACHE_BYTES in assertions to avoid issues on ARM v7 with 128-byte
  cache (due to xdp_rxq_info changing size)
- Only check the tx_lock cache group size for non-debug kernels, rather
  than keeping logic to check its size when DEBUG_LOCK_ALLOC is enabled.
- Link to v2: https://patch.msgid.link/20251105-jk-refactor-queue-stats-v2-0-8652557f9572@intel.com

Changes in v2:
- Fix minor typos.
- Link to v1: https://patch.msgid.link/20251103-jk-refactor-queue-stats-v1-0-164d2ed859b6@intel.com

---
Jacob Keller (9):
      ice: initialize ring_stats->syncp
      ice: use cacheline groups for ice_rx_ring structure
      ice: use cacheline groups for ice_tx_ring structure
      ice: move prev_pkt from ice_txq_stats to ice_tx_ring
      ice: pass pointer to ice_fetch_u64_stats_per_ring
      ice: remove ice_q_stats struct and use struct_group
      ice: use u64_stats API to access pkts/bytes in dim sample
      ice: shorten ring stat names and add accessors
      ice: convert all ring stats to u64_stats_t

 drivers/net/ethernet/intel/ice/ice.h          |   3 -
 drivers/net/ethernet/intel/ice/ice_lib.h      |   6 +
 drivers/net/ethernet/intel/ice/ice_txrx.h     | 135 ++++++++++++-----
 drivers/net/ethernet/intel/ice/ice_txrx_lib.h |   2 +-
 drivers/net/ethernet/intel/ice/ice_base.c     |   4 +-
 drivers/net/ethernet/intel/ice/ice_ethtool.c  |  30 ++--
 drivers/net/ethernet/intel/ice/ice_lib.c      |  61 ++++++--
 drivers/net/ethernet/intel/ice/ice_main.c     | 201 +++++++++++++++++---------
 drivers/net/ethernet/intel/ice/ice_txrx.c     |  45 +++---
 drivers/net/ethernet/intel/ice/ice_txrx_lib.c |   2 +-
 drivers/net/ethernet/intel/ice/ice_xsk.c      |   4 +-
 11 files changed, 331 insertions(+), 162 deletions(-)
---
base-commit: c5acd2847bb5371988d6b5c165b0776967cc7da2
change-id: 20251016-jk-refactor-queue-stats-9e721b34ce01

Best regards,
--  
Jacob Keller <jacob.e.keller@intel.com>