Please, review the fix for:
https://bugs.openjdk.java.net/browse/JDK-8046246
Open hotspot webrevs:
http://cr.openjdk.java.net/~sspitsyn/webrevs/2015/hotspot/8046246-JVMTI-redefscale.1/
Open jdk (new unit test) webrev:
http://cr.openjdk.java.net/~sspitsyn/webrevs/2015/jdk/8046246-JVMTI-manymethods.1/
Summary:
This performance/scalability issue in class redefinition was
reported by HP and the Enterprise Manager team.
The following variants of the adjust_method_entries() functions do
not scale:
ConstantPoolCache::adjust_method_entries()
klassVtable::adjust_method_entries()
klassItable::adjust_method_entries()
InstanceKlass::adjust_default_methods()
The ConstantPoolCache::adjust_method_entries() is the most important.
The approach is to use the holder->method_with_idnum() like this:
Method* new_method =
holder->method_with_idnum(old_method->orig_method_idnum());
if (old_method != new_method) {
<replace old_method with new_method>
}
New algorithm has effectiveness O(M) instead of original O(M^2),
where M is count of methods in the class.
The new test (see webrev above) was used to mesure CPU time
consumed by the
ConstantPoolCache::adjust_method_entries() in both original and
new approach.
The performance numbers are:
---------------------------------------------------------------------------------------
Methods: ------ 1,000 --------------- 10,000 ----------------- 20,000
---------------------------------------------------------------------------------------
Orig: 600,000 nsec (1x) 60,500,000 nsec (~100x)
243,000,000 nsec (~400x)
New: 16,000 nsec (1x) 178,000 nsec (~10x) 355,000
nsec (~20x)
---------------------------------------------------------------------------------------
Testing:
In progress: VM SQE RedefineClasses tests, JTREG
java/lang/instrument, com/sun/jdi tests
Thanks,
Serguei
