Hi Tejun, On Wed, Jan 12, 2022 at 12:24 PM Tejun Heo <tj@xxxxxxxxxx> wrote: > > 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. Fair enough. Apart from needing to expose an rstat flush mechanism to BPF, the main issues that come to mind are conveniently associating with a particular cgroup, and allowing non-root to collect stats independently. Hao's patch series (https://lkml.kernel.org/r/%3C20220112192547.3054575-1-haoluo@xxxxxxxxxx%3E) makes this particularly convenient, but that's a topic for a separate conversation :)
