> He is also the maintainer of JMH, Java Microbenchmarking Harness, a tool I miss in about every other language especially Go. Because writing microbenchmarks is really difficult especially on a JIT that wants to rewritw and optimize things behind your back a couple times. Hotspot can be both brilliant and maddening.

I'm assuming you're aware of the microbenchmarking framework built into Go's testing framework? If so, can you elaborate on where it falls short? I have my own gripes, but it would be nice to understand where others are coming from on this.

> In high performance Java you often rewrite a lot of the base libraries in a very different style that gives you tight control over escape analysis, GC, call site inlining, etc. You actually have a decent amount of control for such a high-level language.

In case you're not aware, the standard Go toolchain does expose some of the optimizations the compiler does, notably escape analysis and bounds check elimination. In the latest release you'll have the option to even export this information as JSON to inspect it programmatically.

Other things, like inlining, are not there (AFAIK), but that's partially because the toolchain is still maturing. For example mid-stack inlining (i.e. inlining any calls to non-leaf functions) is actually a relatively recent addition. Go will also let you choose to not inline something. There's still a lot of work to be done around inlining in general, and visibility into the process would be a nice improvement.

I'd also like to point out that part of the reason the GC has so few knobs has to do with maintainability. Every new knob means expanding the space of configurations significantly, and making sure they all continue to work is a big task. For example, V8 exposes a lot of knobs, but (IIUC) aside from a few default configurations shipped in Chrome, any deviation from those and you're considered "on your own", mainly because of this maintainability problem.

With that being said, I'm not really sure how OpenJDK deals with this issue; maybe there's just enough people out there and enough resources behind the project that it's fine?

> In Go, I haven't been able to find that control. The Go team seems to have taken an opposite approach and removed your control (I often joke about Go just being short for "Go Fuck Yourself" because of its attitude against developer control and the teams's "if we don't need it you don't need it" attitude).

I don't think this is the intended messaging from the Go team, and there's been efforts on their part to shed this image. I think part of it is maturity of the toolchain; Java has nearly 15 years on Go and in some cases there honestly isn't all that much to give visibility into or control over yet. Another part of it is an overall conservative approach toward evolution of the language and of APIs, primarily for long-term maintainability and compatibility. Expanding the API (including performance knobs) usually needs to show a clear net win (see SetMaxHeap, which gives you more control but never really made it in; it still exists as a patch).

> It is resources like this that really make Java shine in its pro high performance developer attitude. (Current Go issue, getting select and channels to operate anywhere remotely efficiently and trying to find a way to keep high CPU goroutines on different OS threads - so far not much luck).

You should definitely file a bug if you have the bandwidth to do so and haven't already. Channels and scheduling should be efficient and smart by default, and finding situations where they make poor decisions is how the runtime improves. The team is fairly responsive to such bugs and even if they don't get resolved immediately, having it on their radar will only help the team make better design decisions going forward.

user:	mknyszek
created:	July 4, 2015
karma:	21