ForkJoin wakeup update

[Aleksey Shipilev]

Hi,

This is the follow up on the different things we can do about FJP
wakeups [1]. First and foremost, I've updated fjp-trace [2] to track
submitter events more accurately, so now we can measure the handoff time
directly, as well as track the unpark cost of the first handoff.

Following Doug's advice, I've did a few experimental changes, described
below:
 * vanilla: plain vanilla FJP
 * wakeup-3: wake up 3 threads instead of 2 during wakeups
 * wakeup-4: wake up 4 threads instead of 2 during wakeups
 * scan-busyloop: replace park in scan() with yield

On the same machine [4], the scores are:
      vanilla: 429 +- 22 us/op
     wakeup-3: 415 +- 15 us/op
     wakeup-4: 390 +- 18 us/op
scan-busyloop: 150 +- 15 us/op

The fjp-trace results with tracing enabled are here [3]. The analysis
for their subtrees follows:

vanilla:
   +60us: first handoff (dominated by unpark)
  +240us: fjp rampup (all threads to wake up)
   +20us: full parallelism
   +15us: catch up (the final completer lags behind?)
   +10us: result handoff

wakeup-3:
   +80us: first handoff (dominated by unpark)
  +180us: fjp rampup (all threads to wake up)
   +40us: full parallelism
   +20us: catch up (the final completer lags behind?)
   +10us: result handoff

wakeup-4:
   +70us: first handoff (dominated by unpark)
  +170us: fjp rampup (all threads to wake up)
   +50us: full parallelism
   +30us: catch up (the final completer lags behind?)
   +10us: result handoff

scan-busyloop:
    +5us: first handoff (nothing to unpark)
   +10us: fjp rampup (pre-balancing)
   +55us: full parallelism
   +10us: catch up (the final completer lags behind?)
   +10us: result handoff

Thanks,
Aleksey.

[1]
http://mail.openjdk.java.net/pipermail/lambda-dev/2012-October/006167.html
[2] https://github.com/shipilev/fjp-trace
[3] http://shipilev.net/pub/jdk/lambda/20121017-fjpwakeup/
[4] 2x8x2 Xeon E5-2680 (SandyBridge) running Solaris 11, and 20121003
lambda nightly with -d64 -XX:-TieredCompilation -XX:+UseParallelOldGC
-XX:+UseNUMA -XX:-UseBiasedLocking -XX:+UseCondCardMark