Re: [RESEND PATCH bpf-next v9 0/5] bpf: rstat: cgroup hierarchical

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

On Wed, Aug 24, 2022 at 5:42 PM Hao Luo <haoluo@google.com> wrote:
>
> On Wed, Aug 24, 2022 at 5:29 PM Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > On Wed, Aug 24, 2022 at 4:31 PM Hao Luo <haoluo@google.com> wrote:
> > >
> > > This patch series allows for using bpf to collect hierarchical cgroup
> > > stats efficiently by integrating with the rstat framework. The rstat
> > > framework provides an efficient way to collect cgroup stats percpu and
> > > propagate them through the cgroup hierarchy.
> > >
> > > The stats are exposed to userspace in textual form by reading files in
> > > bpffs, similar to cgroupfs stats by using a cgroup_iter program.
> > > cgroup_iter is a type of bpf_iter. It walks over cgroups in four modes:
> > > - walking a cgroup's descendants in pre-order.
> > > - walking a cgroup's descendants in post-order.
> > > - walking a cgroup's ancestors.
> > > - process only a single object.
> > >
> > > When attaching cgroup_iter, one needs to set a cgroup to the iter_link
> > > created from attaching. This cgroup can be passed either as a file
> > > descriptor or a cgroup id. That cgroup serves as the starting point of
> > > the walk.
> > >
> > > One can also terminate the walk early by returning 1 from the iter
> > > program.
> > >
> > > Note that because walking cgroup hierarchy holds cgroup_mutex, the iter
> > > program is called with cgroup_mutex held.
> > >
> > > ** Background on rstat for stats collection **
> > > (I am using a subscriber analogy that is not commonly used)
> > >
> > > The rstat framework maintains a tree of cgroups that have updates and
> > > which cpus have updates. A subscriber to the rstat framework maintains
> > > their own stats. The framework is used to tell the subscriber when
> > > and what to flush, for the most efficient stats propagation. The
> > > workflow is as follows:
> > >
> > > - When a subscriber updates a cgroup on a cpu, it informs the rstat
> > >   framework by calling cgroup_rstat_updated(cgrp, cpu).
> > >
> > > - When a subscriber wants to read some stats for a cgroup, it asks
> > >   the rstat framework to initiate a stats flush (propagation) by calling
> > >   cgroup_rstat_flush(cgrp).
> > >
> > > - When the rstat framework initiates a flush, it makes callbacks to
> > >   subscribers to aggregate stats on cpus that have updates, and
> > >   propagate updates to their parent.
> > >
> > > Currently, the main subscribers to the rstat framework are cgroup
> > > subsystems (e.g. memory, block). This patch series allow bpf programs to
> > > become subscribers as well.
> > >
> > > Patches in this series are organized as follows:
> > > * Patches 1-2 introduce cgroup_iter prog, and a selftest.
> > > * Patches 3-5 allow bpf programs to integrate with rstat by adding the
> > >   necessary hook points and kfunc. A comprehensive selftest that
> > >   demonstrates the entire workflow for using bpf and rstat to
> > >   efficiently collect and output cgroup stats is added.
> > >
> > > ---
> > > Changelog:
> > > v8 -> v9:
> > > - Make UNSPEC (an invalid option) as the default order for cgroup_iter.
> > > - Use enum for specifying cgroup_iter order, instead of u32.
> > > - Add BPF_ITER_RESHCED to cgroup_iter.
> > > - Add cgroup_hierarchical_stats to s390x denylist.
> >
> > What 'RESEND' is for?
> > It seems to confuse patchwork and BPF CI.
> >
> > The v9 series made it to patchwork...
> >
> > Please just bump the version to v10 next time.
> > Don't add things to subject, since automation cannot recognize
> > that yet.
>
> Sorry about that. I thought it was RESEND because no content has
> changed. It was just adding an entry in s390 denylist.
>
> Are we good now? Or I need to send a v10?

No need. Assuming that 'RESEND' version will be green in CI.