Re: [RFC PATCH bpf-next 2/9] cgroup: bpf: flush bpf stats on rstat flush

[Tejun Heo <tj@kernel.org>]

On Tue, May 10, 2022 at 12:18:00AM +0000, Yosry Ahmed wrote:
> When a cgroup is popped from the rstat updated tree, subsystems rstat
> flushers are run through the css_rstat_flush() callback. Also run bpf
> flushers for all subsystems that have at least one bpf rstat flusher
> attached, and are enabled for this cgroup.
> 
> A list of subsystems that have attached rstat flushers is maintained to
> avoid looping through all subsystems for all cpus for every cgroup that
> is being popped from the updated tree. Since we introduce a lock here to
> protect this list, also use it to protect rstat_flushers lists inside
> each subsystem (since they both need to locked together anyway), and get
> read of the locks in struct cgroup_subsys_bpf.
> 
> rstat flushers are run for any enabled subsystem that has flushers
> attached, even if it does not subscribe to css flushing through
> css_rstat_flush(). This gives flexibility for bpf programs to collect
> stats for any subsystem, regardless of the implementation changes in the
> kernel.

Yeah, again, the fact that these things are associated with a speicfic
subsystem feels a bit jarring to me. Let's get that resolved first.

Thanks.

-- 
tejun