On Wed, 10 Feb 2021 07:34:59 GMT, Aleksey Shipilev <sh...@openjdk.org> wrote:
>> `JVM_LatestUserDefinedLoader` is called normally from >> `ObjectInputStream.resolveClass` -> `VM.latestUserDefinedLoader0`. And it >> takes a measurable time to walk the stack. There is JDK-8173368 that wants >> to replace it with `StackWalker`, but we can tune up the >> `JVM_LatestUserDefinedLoader` itself without changing the semantics of it >> (thus providing the backportability, including the releases that do not have >> `StackWalker`) and improving performance (thus providing a more aggressive >> baseline for `StackWalker` rewrite). >> >> The key is to recognize that out of two checks: 1) checking for two special >> subclasses; 2) checking for user classloader -- the first one usually >> passes, and second one fails much more frequently. First check also requires >> traversing the superclasses upwards looking for match. Reversing the order >> of the checks, plus inlining the helper method improves performance without >> changing the semantics. >> >> Out of curiosity, my previous patch dropped the first check completely, >> replacing it by asserts, and we definitely run into situation where that >> check is needed on some tests. >> >> On my machine, `VM.latestUserDefinedLoader` invocation time drops from 115 >> to 100 ns/op. Single-threaded SPECjvm2008:serial improves about 3% with this >> patch. >> >> Additional testing: >> - [x] Ad-hoc benchmarks >> - [x] Linux x86_64 fastdebug, `tier1`, `tier2`, `tier3` >> >> --------- >> ### Progress >> - [x] Change must not contain extraneous whitespace >> - [x] Commit message must refer to an issue >> - [ ] Change must be properly reviewed >> >> >> >> ### Download >> `$ git fetch https://git.openjdk.java.net/jdk pull/2485/head:pull/2485` >> `$ git checkout pull/2485` > > Aleksey Shipilev has updated the pull request incrementally with one > additional commit since the last revision: > > Added a comment Looks good. I find it simpler too. You could run the tests with sun.reflect.inflationThreshold=0. Should increase the chance of encountering reflection delegator loaders a lot. Cheers, Thomas ------------- Marked as reviewed by stuefe (Reviewer). PR: https://git.openjdk.java.net/jdk/pull/2485
