Duncan, sorry for that. Updated webrev inplace. Best regards, Vladimir Ivanov
On 1/21/15 1:39 PM, MacGregor, Duncan (GE Energy Management) wrote: > This version seems to have inconsistent removal of ignore profile in the > hotspot patch. It’s no longer added to vmSymbols but is still referenced > in classFileParser. > > On 19/01/2015 20:21, "MacGregor, Duncan (GE Energy Management)" > <duncan.macgre...@ge.com> wrote: > >> Okay, I¹ve done some tests of this with the micro benchmarks for our >> language & runtime which show pretty much no change except for one test >> which is now almost 3x slower. It uses nested loops to iterate over an >> array and concatenate the string-like objects it contains, and replaces >> elements with these new longer string-llike objects. It¹s a bit of a >> pathological case, and I haven¹t seen the same sort of degradation in the >> other benchmarks or in real applications, but I haven¹t done serious >> benchmarking of them with this change. >> >> I shall see if the test case can be reduced down to anything simpler while >> still showing the same performance behaviour, and try add some compilation >> logging options to narrow down what¹s going on. >> >> Duncan. >> >> On 16/01/2015 17:16, "Vladimir Ivanov" <vladimir.x.iva...@oracle.com> >> wrote: >> >>> http://cr.openjdk.java.net/~vlivanov/8063137/webrev.00/hotspot/ >>> http://cr.openjdk.java.net/~vlivanov/8063137/webrev.00/jdk/ >>> https://bugs.openjdk.java.net/browse/JDK-8063137 >>> >>> After GuardWithTest (GWT) LambdaForms became shared, profile pollution >>> significantly distorted compilation decisions. It affected inlining and >>> hindered some optimizations. It causes significant performance >>> regressions for Nashorn (on Octane benchmarks). >>> >>> Inlining was fixed by 8059877 [1], but it didn't cover the case when a >>> branch is never taken. It can cause missed optimization opportunity, and >>> not just increase in code size. For example, non-pruned branch can break >>> escape analysis. >>> >>> Currently, there are 2 problems: >>> - branch frequencies profile pollution >>> - deoptimization counts pollution >>> >>> Branch frequency pollution hides from JIT the fact that a branch is >>> never taken. Since GWT LambdaForms (and hence their bytecode) are >>> heavily shared, but the behavior is specific to MethodHandle, there's no >>> way for JIT to understand how particular GWT instance behaves. >>> >>> The solution I propose is to do profiling in Java code and feed it to >>> JIT. Every GWT MethodHandle holds an auxiliary array (int[2]) where >>> profiling info is stored. Once JIT kicks in, it can retrieve these >>> counts, if corresponding MethodHandle is a compile-time constant (and it >>> is usually the case). To communicate the profile data from Java code to >>> JIT, MethodHandleImpl::profileBranch() is used. >>> >>> If GWT MethodHandle isn't a compile-time constant, profiling should >>> proceed. It happens when corresponding LambdaForm is already shared, for >>> newly created GWT MethodHandles profiling can occur only in native code >>> (dedicated nmethod for a single LambdaForm). So, when compilation of the >>> whole MethodHandle chain is triggered, the profile should be already >>> gathered. >>> >>> Overriding branch frequencies is not enough. Statistics on >>> deoptimization events is also polluted. Even if a branch is never taken, >>> JIT doesn't issue an uncommon trap there unless corresponding bytecode >>> doesn't trap too much and doesn't cause too many recompiles. >>> >>> I added @IgnoreProfile and place it only on GWT LambdaForms. When JIT >>> sees it on some method, Compile::too_many_traps & >>> Compile::too_many_recompiles for that method always return false. It >>> allows JIT to prune the branch based on custom profile and recompile the >>> method, if the branch is visited. >>> >>> For now, I wanted to keep the fix very focused. The next thing I plan to >>> do is to experiment with ignoring deoptimization counts for other >>> LambdaForms which are heavily shared. I already saw problems caused by >>> deoptimization counts pollution (see JDK-8068915 [2]). >>> >>> I plan to backport the fix into 8u40, once I finish extensive >>> performance testing. >>> >>> Testing: JPRT, java/lang/invoke tests, nashorn (nashorn testsuite, >>> Octane). >>> >>> Thanks! >>> >>> PS: as a summary, my experiments show that fixes for 8063137 & 8068915 >>> [2] almost completely recovers peak performance after LambdaForm sharing >>> [3]. There's one more problem left (non-inlined MethodHandle invocations >>> are more expensive when LFs are shared), but it's a story for another >>> day. >>> >>> Best regards, >>> Vladimir Ivanov >>> >>> [1] https://bugs.openjdk.java.net/browse/JDK-8059877 >>> 8059877: GWT branch frequencies pollution due to LF sharing >>> [2] https://bugs.openjdk.java.net/browse/JDK-8068915 >>> [3] https://bugs.openjdk.java.net/browse/JDK-8046703 >>> JEP 210: LambdaForm Reduction and Caching >>> _______________________________________________ >>> mlvm-dev mailing list >>> mlvm-dev@openjdk.java.net >>> http://mail.openjdk.java.net/mailman/listinfo/mlvm-dev >> >> _______________________________________________ >> mlvm-dev mailing list >> mlvm-dev@openjdk.java.net >> http://mail.openjdk.java.net/mailman/listinfo/mlvm-dev > _______________________________________________ mlvm-dev mailing list mlvm-dev@openjdk.java.net http://mail.openjdk.java.net/mailman/listinfo/mlvm-dev
