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 <davidlohr@hp.com>
Acked-by: Darren Hart <dvhart@linux.intel.com>
Cc: Aswin Chandramouleeswaran <aswin@hp.com>
Cc: Darren Hart <dvhart@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jason Low <jason.low2@hp.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott J Norton <scott.norton@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <Waiman.Long@hp.com>
Link: http://lkml.kernel.org/r/1387081917-9102-3-git-send-email-davidlohr@hp.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>