It's becoming more and more apparent to me that HotSpot's defaults, while probably great for typical Java applications, are not so great for e.g. dynamic languages running on the JVM. I think it's time that all the various dynlang implementers pool their shared knowledge of what flags need to be tweaked for better performance, so we can form a better picture of what a fast dynlang hotspot should be.
I'll start. The most recent discovery for us is that -XX:NewRatio=1 performs better than the default 2 on server and 8 on client VMs. Because Ruby is as a rule a lot more object-intensive (having no unboxed numeric types, for example) we really do need a larger young generation. Once transient objects get promoted to older generations the game is over; we're spending all our time collecting Fixnums instead of working. I posted this to hotspot-dev (Paul Hohensee answered but redirected me to hotspot-gc-use) and was told to also consider two additional flags that give the young generation more wiggle room: MaxTenuringThreshold=0-15 ; the number of times an object must survive young gen collections to be promoted; not sure about defaults on client and server or across collectors SurvivorRatio ; Lower values increase the size of the survivor space, allowing more objects to "just die" in the young generation instead of being promoted. I have not tried either of these yet. Anyone else? Any other flags or defaults you've found helpful for performance in your dynlang apps? Here's another from me, which I've posted about previously: -XX:bootclasspath and friends. JRuby is a Ruby implementation, which means it needs to perform reasonably well as a command-line tool. Typical JVM startup precludes fast command-line startup, but it turns out a large portion of that time is spent verifying bytecode. bootclasspath allows JRuby and its dependencies to skip verification, which in our case improved startup time almost 3X, putting it comfortably under 0.5s on OS X. That was a *huge* find, akin to a silver bullet for startup speed. - Cahrlie --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "JVM Languages" group. To post to this group, send email to jvm-languages@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/jvm-languages?hl=en -~----------~----~----~----~------~----~------~--~---
