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Comment by boardwaalk | Hacker News Reader

Interesting article.

I haven't internalized all the parameters of the Go GC, but I wonder if there's a way to tune it on the fly. For example, if I want to run at 60 FPS (16ms/frame), and I've measured that actually doing all the CPU side work took 10ms, can I let the GC have ~5ms of GC time (rather than the <1ms advertised) at the end of my frame to increase throughput (read: less cycles burned overtime & better power efficiency)?

If not in Go, can I do this elsewhere like on the JVM?

Hopefully this isn't too off topic (since the article is about trade-offs of throughput vs latency).

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That's a realtime GC and yes, you can buy a JVM from IBM that has one, they call it the Metronome collector:

http://researcher.watson.ibm.com/researcher/view_group_subpa...

Metronome has pause time in the hundreds of microseconds range. The tradeoff it makes is that, amongst other things, it requires read barriers i.e. every time you read a pointer from the heap you have to execute some extra code to interact with the GC subsystem. If you think about how often you read pointers from the heap in a typical program, well, that turns into a lot of barriers and a corresponding execution performance hit.

Per the linked article, if their claims are to be trusted, the barrier overhead is only 4%, which is amazingly low. Low enough that it's inconsequential for any application actually needing low pause times, if the claims are correct, which I unfortunately do not know.

Funnny, I remember years ago reading one of the patents the GC is probably based on, and thinking the entire thing was brilliant.

FWIW, Go 1.8's GC uses essentially the same techniques as Metronome.

I don't think you can do it with Go. But you can do it with Nim for example, there if you set 3 ms max GC time you have guarantee that you will only get 3ms of GC time. You can set max time for Java GC also, but from what I seen it's not so strict on G1 collector.

Is there a way to ensure that the amount of time you set aside for GC is, err, enough? I imagine the outcome of it being insufficient would be quite bad... eventually.

I don't recall a lot about it, but what you described is "real-time garbage collection". If you google that term, you should find some work/writeups related to it :)

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