Re: [PATCH 1/2] cgroup: add cpu.stat_percpu

[Tejun Heo <tj@kernel.org>]

Hello,

On Tue, Jan 11, 2022 at 03:38:20PM -0800, Josh Don wrote:
> Is the concern there just the extra overhead from making multiple
> trips into this handler and re-allocating the buffer until it is large
> enough to take all the output? In that case, we could pre-allocate
> with a size of the right order of magnitude, similar to /proc/stat.
> 
> Lack of per-cpu stats is a gap between cgroup v1 and v2, for which v2
> can easily support this interface given that it already tracks the
> stats percpu internally. I opted to dump them all in a single file
> here, to match the consolidation that occurred from cpuacct->cpu.stat.

Yeah, nack on this. That part was dropped intentionally. These text pseudo
files aren't a great medium for this sort of (potentially large) data dump
and they scale really badly with new fields which we may want to expose in
the future. For detailed introspection, a better route would be using bpf
and if that's inconvenient for some reason trying to make them more
convenient.

Thanks.

-- 
tejun