I for one would love it. Cheers, Mario
2015-06-22 20:48 GMT+02:00 Jeremy Manson <jeremyman...@google.com>: > Hey folks, > > (cc'ing Aleksey and John, because I mentioned this to them at the JVMLS last > year, but I never followed up.) > > We have a patch at Google I've always wanted to contribute to OpenJDK, but I > always figured it would be unwanted. I've recently been thinking that might > not be as true, though. I thought I would ask if there is any interest / if > I should write a JEP / if I should just forget it. > > The basic problem is that there is no low-overhead supported way to figure > out where allocation hotspots are. That is, sets of stack traces where lots > of allocation / large allocations took place. > > What I had originally done (this was in ~2007) was use bytecode rewriting to > instrument allocation sites. The instrumentation would call a Java method, > and the method would capture a stack trace. To reduce overhead, there was a > per-thread counter that only took a stack trace once every N bytes > allocated, where N is a randomly chosen point in a probability distribution > that centered around ~512K. > > This was *way* too slow, and it didn't pick up allocations through JNI, so I > instrumented allocations at the VM level, and the overhead went away. The > sampling is always turned on in our internal VMs, and a user can just query > an interface for a list of sampled stack traces. The allocated stack traces > are held with weak refs, so you only get live samples. > > The additional overhead for allocations amounts to a subtraction, and an > occasional stack trace, which is usually a very, very small amount of our > CPU (although I had to do some jiggering in JDK8 to fix some performance > regressions). > > There really isn't another good way to do this with low overhead. I was > wondering how the gruop would feel about our contributing it? > > Thoughts? > > Jeremy -- pgp key: http://subkeys.pgp.net/ PGP Key ID: 80F240CF Fingerprint: BA39 9666 94EC 8B73 27FA FC7C 4086 63E3 80F2 40CF Java Champion - Blog: http://neugens.wordpress.com - Twitter: @neugens Proud GNU Classpath developer: http://www.classpath.org/ OpenJDK: http://openjdk.java.net/projects/caciocavallo/ Please, support open standards: http://endsoftpatents.org/
