RFR: 8276662: Scalability bottleneck in SymbolTable::lookup_common()

[Aleksey Shipilev]

On Tue, 16 Nov 2021 19:02:20 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> ```
> diff --git a/src/hotspot/share/classfile/symbolTable.cpp b/src/hotspot/share/classfile/symbolTable.cpp
> index fa966fc7b22..edf48a2c2c1 100644
> --- a/src/hotspot/share/classfile/symbolTable.cpp
> +++ b/src/hotspot/share/classfile/symbolTable.cpp
> @@ -93,3 +93,3 @@ static volatile bool   _has_items_to_clean = false;
>  static volatile bool _alt_hash = false;
> -static volatile bool _lookup_shared_first = false;
> +static THREAD_LOCAL bool _lookup_shared_first = false;
> ```

Woot, I think it works and even the simple "Hello World" startup seems to respond:


$ perf stat -r 1000 build/server-baseline/bin/java -Xms128m -Xmx128m Hello > /dev/null

 Performance counter stats for 'build/server-baseline/bin/java -Xms128m -Xmx128m Hello' (1000 runs):

             29.62 msec task-clock                #    1.165 CPUs utilized            ( +-  0.11% )
                93      context-switches          #    0.003 M/sec                    ( +-  0.14% )
                 0      cpu-migrations            #    0.010 K/sec                    ( +-  6.36% )
             2,608      page-faults               #    0.088 M/sec                    ( +-  0.01% )
        83,596,348      cycles                    #    2.822 GHz                      ( +-  0.22% )  (46.41%)
        10,204,346      stalled-cycles-frontend   #   12.21% frontend cycles idle     ( +-  0.40% )  (43.73%)
        28,164,763      stalled-cycles-backend    #   33.69% backend cycles idle      ( +-  0.36% )  (45.36%)
        63,232,465      instructions              #    0.76  insn per cycle         
                                                  #    0.45  stalled cycles per insn  ( +-  0.10% )  (53.59%)
        12,144,831      branches                  #  409.979 M/sec                    ( +-  0.11% )  (56.27%)
           448,789      branch-misses             #    3.70% of all branches          ( +-  0.25% )  (54.64%)

         0.0254298 +- 0.0000362 seconds time elapsed  ( +-  0.14% )

$ perf stat -r 1000 build/linux-x86_64-server-release/images/jdk/bin/java -Xms128m -Xmx128m Hello > /dev/null

 Performance counter stats for 'build/linux-x86_64-server-release/images/jdk/bin/java -Xms128m -Xmx128m Hello' (1000 runs):

             29.22 msec task-clock                #    1.166 CPUs utilized            ( +-  0.11% )
                93      context-switches          #    0.003 M/sec                    ( +-  0.14% )
                 0      cpu-migrations            #    0.009 K/sec                    ( +-  6.53% )
             2,605      page-faults               #    0.089 M/sec                    ( +-  0.01% )
        81,731,944      cycles                    #    2.797 GHz                      ( +-  0.24% )  (46.56%)
        10,163,520      stalled-cycles-frontend   #   12.44% frontend cycles idle     ( +-  0.40% )  (43.32%)
        26,563,080      stalled-cycles-backend    #   32.50% backend cycles idle      ( +-  0.36% )  (44.87%)
        63,660,354      instructions              #    0.78  insn per cycle         
                                                  #    0.42  stalled cycles per insn  ( +-  0.09% )  (53.44%)
        12,049,198      branches                  #  412.400 M/sec                    ( +-  0.12% )  (56.68%)
           447,857      branch-misses             #    3.72% of all branches          ( +-  0.22% )  (55.13%)

         0.0250630 +- 0.0000353 seconds time elapsed  ( +-  0.14% )

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

PR: https://git.openjdk.java.net/jdk/pull/6400