[PATCH v2 0/3] kernel: lockless wake-queues

[Davidlohr Bueso <dave@stgolabs.net>]

Hello,

This series is aimed at addressing some of the futex hash bucket
lock hold times by introducing lockless wake-queues for futex_wake.

patch-1: introduces the lockless wake-queue machinery.
patch-2: makes use of patch 1 for futexes.
patch-3: makes use of patch 1 for posix mqueues.

Details in the individual patches.

This was suggested sometime ago by peterz, but due to it potentially
causing spurious wakeups, was never given much consideration. However,
nowadays, so far, I am reliably booting a 45-core box with peterz's
patch to trigger spurious wakeups. While there are drivers out there
that do not play nice with schedule(), they can be fixed over time --
while this is a production problem for some customers). Furthermore,
after some auditing, there really aren't that many, it a lot of cases,
those functions that end up calling schedule are merely wrapped in a
loop, so just not clear at first sight.

Changes from v1:
	- Simplify wake_q and more comments, suggested by George Spelvin.
	- Made it very clear in the comments that this can cause spurious
	  wakeups, and how naughty users should handle them. (Linus)
	- Added mqueue user as this was also wanted for rt purposes.

Applies on top of Linus' tree 4.0-rc1 (4a152c3913f). Thanks!

  sched: lockless wake-queues
  futex: lockless wakeups
  ipc/mqueue: lockless pipelined wakeups

 include/linux/sched.h | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 ipc/mqueue.c          | 50 +++++++++++++++++++++++++++++++-------------------
 kernel/futex.c        | 33 +++++++++++++++++----------------
 kernel/sched/core.c   | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 140 insertions(+), 35 deletions(-)

--
2.1.4