On Wed, Aug 24, 2022 at 5:42 PM Hao Luo <haoluo@xxxxxxxxxx> wrote: > > On Wed, Aug 24, 2022 at 5:29 PM Alexei Starovoitov > <alexei.starovoitov@xxxxxxxxx> wrote: > > > > On Wed, Aug 24, 2022 at 4:31 PM Hao Luo <haoluo@xxxxxxxxxx> 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.
