[PATCH 0/2] locking/percpu-rwsem: Optimizations/tweaks

[Peter Zijlstra]

As reported by John and Dmitry, Android tickles bad behaviour in
cgroup_threadgroup_rwsem.

These two patches attempt to address the issue by optimizing the percpu-rwsem
slow path and second add a bias knob to the percpu-rwsem that allows disabling
the fast path which improves writer latency by getting rid of a
synchronize_sched() call.

---
 fs/super.c                    |   3 +-
 include/linux/percpu-rwsem.h  |  96 +++++++++++++++--
 kernel/cgroup.c               |   2 +-
 kernel/locking/percpu-rwsem.c | 246 +++++++++++++++++++++++++-----------------
 4 files changed, 239 insertions(+), 108 deletions(-)