automaxprocs VS lxcfs

We use https://github.com/uber-go/automaxprocs after we joyfully discovered that Go assumed we had the entire cluster's cpu count on any particular pod. Made for some very strange performance characteristics in scheduling goroutines.

Follow notable issues on https://github.com/golang/go to understand such things like why https://github.com/uber-go/automaxprocs was created.

Please never set the value manually in a kubernetes production environment. Use https://github.com/uber-go/automaxprocs

There is an environment variable (GOMAXPROCS) that you can set which determines how many threads your go program will use simultaneously. You can use this great library from Uber to automatically set the GOMAXPROCS variable to match a Linux container CPU quota. If you are running Go workloads in Kubernetes, you should use this.

AFAIK, it hasn't changed, this exact situation with cgroups is still something I have to tell fellow developers about. Some of them have started using [automaxprocs] to automatically detect and set.

[automaxprocs]: https://github.com/uber-go/automaxprocs

For you own applications, you can use: https://github.com/uber-go/automaxprocs

> I wondered for a while if docker could make a fake /proc/cpuinfo

This exists: https://github.com/lxc/lxcfs

lxcfs is a FUSE filesystem that mocks /proc by inferring cgroup values in a way that makes other applications and libraries work without having to care about whether it runs in a container (to the best of its ability - there are definitely caveats).

One such example is that /proc/uptime should reflect the uptime of the container, not the host; additionally /proc/cpuinfo reflects the number of CPUs as a combination of cpu.max and cpuset.cpus (whichever the lower bound is).

As others also mentioned, inferring the number of CPUs could also be done using the sched_getaffinity syscall - this doesn't depend on /proc/cpuinfo, so depending on the library you're using you might be in a pickle.