RFR: Disable biased locking by default

[Aleksey Shipilev]

Hi,

I think it makes sense to disable biased locking by default:

$ hg diff
diff -r d64a5a4a4366 src/share/vm/runtime/arguments.cpp
--- a/src/share/vm/runtime/arguments.cpp	Mon Sep 04 22:35:03 2017 +0200
+++ b/src/share/vm/runtime/arguments.cpp	Tue Sep 05 19:43:21 2017 +0200
@@ -2075,6 +2075,14 @@
     }
     FLAG_SET_DEFAULT(ShenandoahUncommitDelay, max_uintx);
   }
+
+  // Current Hotspot machinery for biased locking may introduce lots of latency hiccups
+  // that negate the benefits of low-latency GC. The throughput improvements granted by
+  // biased locking on modern hardware are not covering the latency problems induced by
+  // it. Therefore, unless user really wants it, disable biased locking.
+  if (FLAG_IS_DEFAULT(UseBiasedLocking)) {
+    FLAG_SET_DEFAULT(UseBiasedLocking, false);
+  }
 }

 void Arguments::set_gc_specific_flags() {


Testing: hotspot_gc_shenandoah

Thanks,
-Aleksey