When running Java-based tools, use -XX:+TieredCompilation -XX:TieredStopAtLevel=1 instead of -client, as the latter is ignored on 64-bit JVMs since at least JDK 6.

The new flags have been shown to cut down CPU time by 50% due to reduced time spent in JIT and improving overall run time for short running actions, some times also cutting them in half.

Here's a benchmark of Bazel building itself, giving a nice 2-4x speedup:

./output/bazel clean && ./output/bazel build //src:bazel

Bazel before this change:
INFO: Elapsed time: 197.783s, Critical Path: 194.10s
INFO: Elapsed time: 198.928s, Critical Path: 195.65s
INFO: Elapsed time: 194.913s, Critical Path: 191.56s

Bazel before this change with --strategy=Javac=worker:
INFO: Elapsed time: 130.436s, Critical Path: 124.27s
INFO: Elapsed time: 116.114s, Critical Path: 112.30s
INFO: Elapsed time: 116.852s, Critical Path: 84.45s

Bazel with this change:
INFO: Elapsed time: 121.625s, Critical Path: 119.08s
INFO: Elapsed time: 119.401s, Critical Path: 115.80s
INFO: Elapsed time: 121.198s, Critical Path: 119.03s

Bazel with this change and --strategy=Javac=worker:
INFO: Elapsed time: 54.456s, Critical Path: 51.28s
INFO: Elapsed time: 53.272s, Critical Path: 51.09s
INFO: Elapsed time: 52.966s, Critical Path: 49.86s

Bazel with this change and --strategy=Javac=worker and stripping -XX:TieredStopAtLevel=1 from JVM flags when using workers:
INFO: Elapsed time: 61.599s, Critical Path: 58.93s
INFO: Elapsed time: 48.695s, Critical Path: 45.02s
INFO: Elapsed time: 46.874s, Critical Path: 43.91s
INFO: Elapsed time: 46.174s, Critical Path: 43.32s

(The latter is a possible optimization for workers and it's also nice to know that the limited tiered compilation does not hurt their performance.)

--
MOS_MIGRATED_REVID=125448089

1 files changed, 8 insertions, 2 deletions

diff --git a/src/java_tools/buildjar/BUILD b/src/java_tools/buildjar/BUILD
index 56298dfd1a..dc16a42940 100644
--- a/src/java_tools/buildjar/BUILD
+++ b/src/java_tools/buildjar/BUILD
@@ -54,7 +54,10 @@ java_toolchain(
     ijar = ["//third_party/ijar"],
     javabuilder = ["bootstrap_deploy.jar"],
     javac = ["//third_party/java/jdk/langtools:javac_jar"],
-    jvm_opts = ["-client"],
+    jvm_opts = [
+        "-XX:+TieredCompilation",
+        "-XX:TieredStopAtLevel=1",
+    ],
     singlejar = ["//src/java_tools/singlejar:bootstrap_deploy.jar"],
     source_version = "8",
     target_version = "8",
@@ -70,7 +73,10 @@ java_toolchain(
     ijar = ["//third_party/ijar"],
     javabuilder = ["//third_party/java/jdk/javabuilder:JavaBuilder_0.1.0"],
     javac = ["//third_party/java/jdk/langtools:javac7_jar"],
-    jvm_opts = ["-client"],
+    jvm_opts = [
+        "-XX:+TieredCompilation",
+        "-XX:TieredStopAtLevel=1",
+    ],
     singlejar = ["//src/java_tools/singlejar:bootstrap_deploy.jar"],
     source_version = "7",
     target_version = "7",