RFR [14]: 8231707: Improve Mutex inlining

Claes Redestad claes.redestad at oracle.com
Wed Oct 2 14:56:51 UTC 2019


gcc thinks Mutex::lock(Thread*) is too big to be inlined into
Mutex::lock(), which means we often do an extra call when grabbing a
mutex. By outlining the contended loop into a separate method, then
(uncontended) lock(Thread*) gets inlined into lock(), which means
uncontended mutex locking will perform one less call. This speeds
things up somewhat in targetted microbenchmarks[1].

Webrev: http://cr.openjdk.java.net/~redestad/8231707/open.00/
Bug:    https://bugs.openjdk.java.net/browse/JDK-8231707

Robbin Ehn and I also did a more elaborate experiment[2] to make
Mutex::lock/try_lock/... inlineable in full. This interestingly does
slightly worse on the targetted micro, while increasing the size
of the JVM more aggressively.

Test: tier1-3



  Reference.hasReferencePendingList will use a mutex in the VM:

            Mode  Cnt   Score   Error  Units
  baseline  avgt   20  70.913 ± 2.381  ns/op
  patch     avgt   20  61.014 ± 3.545  ns/op

  [2] http://cr.openjdk.java.net/~redestad/8231707/alternative.00
            avgt   20  63.150 ± 4.135  ns/op

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