[PATCH v4 next 0/9] locking/osq_lock: Optimisations to osq_lock code

[David Laight <david.laight.linux@gmail.com>]

This is a continuation of some patches I wrote over two years ago.
They go a lot further and reduce the per-cpu data to a structure
that only contains two cpu numbers.

I've fixed some broken/missing memory barriers but left the initial xchg()
when acquiring the lock as a full barrier, I think it could be relaxed.

Tested with a userspace harness that can conditionally sleep at various points.

David Laight (9):
  locking/osq_lock: Add some comments about how it works
  locking/osq_lock: Save the cpu number for 'prev' not the node address
  locking/osq_lock: Set prev_cpu=0 instead of locked=1
  locking/osq_lock: Delete 'fast path' code from osq_unlock()
  locking/osq_lock: Avoid writing to node->next in the osq_lock() fast
    path
  locking/osq: Use cpu number for 'next' pointer
  locking/osq: Use 'unsigned int' for next/prev/tail
  locking/osq: inline encode_cpu() and rename decode_cpu()
  locking/osq_lock: Swap next<->prev and tail<->head

 include/linux/osq_lock.h  |  10 +-
 kernel/locking/osq_lock.c | 286 ++++++++++++++++++++------------------
 2 files changed, 154 insertions(+), 142 deletions(-)

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2.39.5