How to count Linux CPU cores with large CPU masks?

[kubo39]

Unfortunately, cpu_set_t is not enough for very large CPU maks.

Case study

• golang

• allocate 8kB buffer on stack. (8k is the maximum number of cpus supported by Linux 3.17)

• Ruby

• allocate buffer on heap step by step(64 -> 128 -> ... -> 16384), return when the counted cores >= 1.

[seanmonstar]

O_O

A stack buffer sounds better, though I'd worry that doing so would slow down the common case (how common is it to have more than 64 cpus?). It could perhaps be a #[cold] function that is used if the cpu_set_t wasn't big enough.