Messages in this thread | | | Date | Wed, 27 Jul 2022 22:51:16 -0700 | Subject | Re: [PATCH bpf-next v5 8/8] bpf: add a selftest for cgroup hierarchical stats collection | From | Yonghong Song <> |
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On 7/22/22 10:48 AM, Yosry Ahmed wrote: > Add a selftest that tests the whole workflow for collecting, > aggregating (flushing), and displaying cgroup hierarchical stats. > > TL;DR: > - Userspace program creates a cgroup hierarchy and induces memcg reclaim > in parts of it. > - Whenever reclaim happens, vmscan_start and vmscan_end update > per-cgroup percpu readings, and tell rstat which (cgroup, cpu) pairs > have updates. > - When userspace tries to read the stats, vmscan_dump calls rstat to flush > the stats, and outputs the stats in text format to userspace (similar > to cgroupfs stats). > - rstat calls vmscan_flush once for every (cgroup, cpu) pair that has > updates, vmscan_flush aggregates cpu readings and propagates updates > to parents. > - Userspace program makes sure the stats are aggregated and read > correctly. > > Detailed explanation: > - The test loads tracing bpf programs, vmscan_start and vmscan_end, to > measure the latency of cgroup reclaim. Per-cgroup readings are stored in > percpu maps for efficiency. When a cgroup reading is updated on a cpu, > cgroup_rstat_updated(cgroup, cpu) is called to add the cgroup to the > rstat updated tree on that cpu. > > - A cgroup_iter program, vmscan_dump, is loaded and pinned to a file, for > each cgroup. Reading this file invokes the program, which calls > cgroup_rstat_flush(cgroup) to ask rstat to propagate the updates for all > cpus and cgroups that have updates in this cgroup's subtree. Afterwards, > the stats are exposed to the user. vmscan_dump returns 1 to terminate > iteration early, so that we only expose stats for one cgroup per read. > > - An ftrace program, vmscan_flush, is also loaded and attached to > bpf_rstat_flush. When rstat flushing is ongoing, vmscan_flush is invoked > once for each (cgroup, cpu) pair that has updates. cgroups are popped > from the rstat tree in a bottom-up fashion, so calls will always be > made for cgroups that have updates before their parents. The program > aggregates percpu readings to a total per-cgroup reading, and also > propagates them to the parent cgroup. After rstat flushing is over, all > cgroups will have correct updated hierarchical readings (including all > cpus and all their descendants). > > - Finally, the test creates a cgroup hierarchy and induces memcg reclaim > in parts of it, and makes sure that the stats collection, aggregation, > and reading workflow works as expected. > > Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Let us tag the subject with "selftests/bpf: Add a selftest ..." instead of "bpf: add a selftest ..."
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