RFR: 8283566: G1: Improve G1BarrierSet::enqueue performance

[Aleksey Shipilev]

While looking at startup/warmup benchmarks for VarHandles, I noticed that `G1BarrierSet::enqueue` is not inlined and quite hot. Its uses also load the oop first, and then check if queues are active. This could be improved a bit. This only matters for the barrier paths that VM takes, which is the case for `java.lang.invoke` VM infra. 

Not sure about `enqueue_oop` name, I did it to avoid accidental overload clash with `enqueue(T* dst)`. Open for suggestions.

On a simple test:


import java.lang.invoke.MethodHandles;
import java.lang.invoke.VarHandle;

public class VHWarmup {

    static final int SIZE = 1_000_000;

    private VarHandle[] vhs;
    private int x;

    public static void main(String... args) throws Exception {
        new VHWarmup().run();
    }

    public void run() throws Exception {
        vhs = new VarHandle[SIZE];
        for (int c = 0; c < SIZE; c++) {
            VarHandle vh = MethodHandles.lookup().findVarHandle(VHWarmup.class, "x", int.class);
            vh.get(this);
            vhs[c] = vh;
        }
    }
}


Baseline:


$ perf stat -r 10 build/linux-x86_64-server-release/images/jdk/bin/java -Xms128m -Xmx128m VHWarmup > /dev/null

 Performance counter stats for 'build/linux-x86_64-server-release/images/jdk/bin/java -Xms128m -Xmx128m VHWarmup' (10 runs):

          1,392.13 msec task-clock                #    1.183 CPUs utilized            ( +-  0.45% )
               887      context-switches          #    0.637 K/sec                    ( +-  1.05% )
                 6      cpu-migrations            #    0.004 K/sec                    ( +- 14.72% )
            31,755      page-faults               #    0.023 M/sec                    ( +-  0.17% )
     4,708,582,477      cycles                    #    3.382 GHz                      ( +-  0.44% )  (50.46%)
       168,230,638      stalled-cycles-frontend   #    3.57% frontend cycles idle     ( +-  2.75% )  (50.35%)
       790,033,580      stalled-cycles-backend    #   16.78% backend cycles idle      ( +-  1.82% )  (50.03%)
     9,094,235,238      instructions              #    1.93  insn per cycle         
                                                  #    0.09  stalled cycles per insn  ( +-  0.22% )  (49.54%)
     1,716,367,002      branches                  # 1232.909 M/sec                    ( +-  0.38% )  (49.65%)
         3,908,772      branch-misses             #    0.23% of all branches          ( +-  2.89% )  (49.97%)

           1.17642 +- 0.00616 seconds time elapsed  ( +-  0.52% )


Patched:


$ perf stat -r 10 build/linux-x86_64-server-release/images/jdk/bin/java -Xms128m -Xmx128m VHWarmup > /dev/null

 Performance counter stats for 'build/linux-x86_64-server-release/images/jdk/bin/java -Xms128m -Xmx128m VHWarmup' (10 runs):

          1,288.69 msec task-clock                #    1.203 CPUs utilized            ( +-  0.73% )
               860      context-switches          #    0.667 K/sec                    ( +-  1.38% )
                 7      cpu-migrations            #    0.006 K/sec                    ( +- 11.96% )
            31,830      page-faults               #    0.025 M/sec                    ( +-  0.13% )
     4,331,508,315      cycles                    #    3.361 GHz                      ( +-  0.72% )  (50.01%)
       151,638,797      stalled-cycles-frontend   #    3.50% frontend cycles idle     ( +-  2.94% )  (49.56%)
       604,797,159      stalled-cycles-backend    #   13.96% backend cycles idle      ( +-  4.17% )  (49.70%)
     8,517,580,297      instructions              #    1.97  insn per cycle         
                                                  #    0.07  stalled cycles per insn  ( +-  0.50% )  (49.99%)
     1,600,179,319      branches                  # 1241.714 M/sec                    ( +-  0.46% )  (50.44%)
         4,129,679      branch-misses             #    0.26% of all branches          ( +-  4.39% )  (50.30%)

           1.07125 +- 0.00822 seconds time elapsed  ( +-  0.77% )


Additional testing:
 - [ ] Linux x86_64 fastdebug `tier1`
 - [ ] More benchmarks

-------------

Commit messages:
 - Cleanups
 - More complete patch
 - Inlining

Changes: https://git.openjdk.java.net/jdk/pull/7921/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7921&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283566
  Stats: 41 lines in 4 files changed: 26 ins; 10 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7921.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7921/head:pull/7921

PR: https://git.openjdk.java.net/jdk/pull/7921