perf bench: Add futex-wake microbenchmark

Block a bunch of threads on a futex and wake them up, N at a time.

This program is particularly useful to measure the latency of nthread
wakeups in non-error situations:  all waiters are queued and all wake
calls wakeup one or more tasks.

An example run:

  $ perf bench futex wake -t 512 -r 100
  Run summary [PID 27823]: blocking on 512 threads (at futex 0x7e10d4), waking up 1 at a time.

  [Run 1]: Wokeup 512 of 512 threads in 6.0080 ms
  [Run 2]: Wokeup 512 of 512 threads in 5.2280 ms
  [Run 3]: Wokeup 512 of 512 threads in 4.8300 ms
  ...
  [Run 100]: Wokeup 512 of 512 threads in 5.0100 ms
  Wokeup 512 of 512 threads in 5.0109 ms (+-2.25%)

Signed-off-by: Davidlohr Bueso <[email protected]>
Acked-by: Darren Hart <[email protected]>
Cc: Aswin Chandramouleeswaran <[email protected]>
Cc: Darren Hart <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jason Low <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Scott J Norton <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Waiman Long <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

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