[jrockway]

I am guessing the API isn't stable enough for letting the runtime set maxprocs. I use https://pkg.go.dev/go.uber.org/automaxprocs and have had to update it periodically because Redhat and Debian have different defaults. (Should one even run k8s on Redhat? I say no, but Redhat says yes. That's how I know about this.)

This, I think, is cgroups 1 vs. cgroups 2 and everyone should have cgroups 2 now, but ... it would feel weird for the Go runtime to decide on one. To me, anyway.

[__turbobrew__]

Which API is not stable? Cgroupfs?

I would think that cgroupfs is considered an API to userspace and therefore it shouldn’t break in the future? Hence creating cgroups v2?

I have written code which handles both cgroups v1 and cgroups v2, it isn’t terribly hard. Golang could also only support setting automatic parameters when running in cgroups v2 if that made things easier.

For a language that prides itself in sane defaults I think they have missed the mark here. I could probably add support to the golang runtime in a few hundred lines of code and probably save millions of dollars and megawatts of energy because the go runtime is not spawning 50 processes to run a program which is constrained to 1 core.

[kbolino]

The OpenJDK folks have quite a long and storied history of trying to do this right and still generally recommend that if you want a JVM to have the right number of CPUs, you should set the relevant parameter yourself (-XX:ActiveProcessorCount). This is basically the same advice as Go folks telling you to set GOMAXPROCS yourself.

The problem is not just cgroups v1 vs cgroups v2 or the stability of cgroupfs, but also of CPU "shares" vs "limits", the different tunables for different Linux schedulers, the effective limits under hierarchical cgroups, etc.

[ljm]

I’m not 100% sold on the idea that Go’s defaults are sane.

They’re highly opinionated and not really that intuitive.

[throw-the-towel]

Could you elaborate?