I agree it's a good and well written talk. I enjoyed reading it.

WRT knobs. Apparently they aren't going to do so, but I suspect that's a mistake.

It's apparent from reading this talk that GC design for Go has often been constrained by this "no knobs" design philosophy in ways that seem problematic. For instance they designed a GC to have the shortest pauses possible, but then kept hitting throughput problems on a classic batch job where latency doesn't matter at all (their compiler).

I wrote about this problem some time ago:

https://blog.plan99.net/modern-garbage-collection-911ef4f8bd...

The essay points out that GC tuning exists because of fundamental tradeoffs between low pause times and throughput. Java lets you tune the GC precisely to avoid the nasty situation Go got itself into, where the demands of very very different kinds of workload (super latency sensitive Google servers vs compilers) are difficult to reconcile with each other.

You can see this tension come through several times, like when they admit that they would have done a normal "enterprise" style GC as they rather condescendingly called it, but they felt Go's market position was under threat, they only had a year to make improvements but were constrained by the requirement to not slow down the Go compiler itself:

So we were limited. We had basically a year of compiler performance improvements that we could eat up by making the GC concurrent. But that was it. We couldn't slow down Go programs. That would have been untenable in 2014 ... Go also desperately needed short term success in 2015.

So they ended up with this design that they knew was kind of weird and not that great, but it let them promote low latency above all else to their users, and they sort of buried the tradeoffs they were making along the way. Which, reading between the lines, might have been related to internal staffing issues at Google - why else would a well funded project like Go have "desperately needed short term success in 2015"? It's not like they sell the Go compiler.

More quotes that support this:

As you can see if you have [request oriented collector] on and not a lot of sharing, things actually scale quite nicely. If you don't have ROC on it wasn't nearly as good.

So they had a GC that scaled better. But it got killed by, you guessed it, the needs of batch jobs:

But that wasn't good enough, we also had to make sure that ROC didn't slow down other pieces of the system. At that point there was a lot of concern about our compiler and we could not slow down our compilers. Unfortunately the compilers were exactly the programs that ROC did not do well at. We were seeing 30, 40, 50% and more slowdowns and that was unacceptable. Go is proud of how fast its compiler is so we couldn't slow the compiler down, certainly not this much.

They could have solved this problem by having two GCs for Go programs tuned for throughput and latency, or doing what the Java guys did and trying to make an adaptive GC like G1 where you can give it pause time targets: if the target is very high then it tunes for throughput otherwise it tunes for latency. But instead they seem to have sacrificed it all on the altar of "no knobs", which is a pity because they ended up introducing two knobs anyway: SetGCPercent and SetMaxHeap.

Well hey, guess what, if you use the G1 GC in Java you are only supposed to tweak two knobs too - max heap size (same as Go) and pause time target. If anything G1's knobs seem better because pause time target is a lot easier for developers to reason about than "heap overhead multiplier". In the end it's unclear their sacrifices were really worth it, although I don't know enough about Go to know what dire straits in 2015 were causing them to need such short term success.