[PATCH -tip 0/4] locking/rwsem (xadd): Reader waiter optimizations

[Davidlohr Bueso]

Hi,

This is a follow up series while reviewing Waiman's reader-owned
state work[1]. While I have based it on -tip instead of that change,
I can certainly rebase the series in some future iteration.

Changes are mainly around reader-waiter optimizations, in no particular
order. Has passed numerous DB benchmarks without things falling apart
for a 8 core Westmere doing page allocations (page_test) in aim9:

aim9
         4.6-rc6				4.6-rc6
						rwsemv2
Min      page_test   378167.89 (  0.00%)   382613.33 (  1.18%)
Min      exec_test      499.00 (  0.00%)      502.67 (  0.74%)
Min      fork_test     3395.47 (  0.00%)     3537.64 (  4.19%)
Hmean    page_test   395433.06 (  0.00%)   414693.68 (  4.87%)
Hmean    exec_test      499.67 (  0.00%)      505.30 (  1.13%)
Hmean    fork_test     3504.22 (  0.00%)     3594.95 (  2.59%)
Stddev   page_test    17426.57 (  0.00%)    26649.92 (-52.93%)
Stddev   exec_test        0.47 (  0.00%)        1.41 (-199.05%)
Stddev   fork_test       63.74 (  0.00%)       32.59 ( 48.86%)
Max      page_test   429873.33 (  0.00%)   456960.00 (  6.30%)
Max      exec_test      500.33 (  0.00%)      507.66 (  1.47%)
Max      fork_test     3653.33 (  0.00%)     3650.90 ( -0.07%)

             4.6-rc6     4.6-rc6
                         rwsemv2
User            1.12        0.04
System          0.23        0.04
Elapsed       727.27      721.98

[1] http://permalink.gmane.org/gmane.linux.kernel/2216743

Thanks!

Davidlohr Bueso (4):
  locking/rwsem: Avoid stale ->count for rwsem_down_write_failed()
  locking/rwsem: Drop superfluous waiter refcount
  locking/rwsem: Enable lockless waiter wakeup(s)
  locking/rwsem: Rework zeroing reader waiter->task

 kernel/locking/rwsem-xadd.c | 74 ++++++++++++++++++++++++++-------------------
 1 file changed, 43 insertions(+), 31 deletions(-)

-- 
2.8.1