+cc Michal Koutný <mkoutny@xxxxxxxx> On Fri, Jun 10, 2022 at 12:44 PM Yosry Ahmed <yosryahmed@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 two modes: > > - walking a cgroup's descendants. > - walking a cgroup's ancestors. > > When attaching cgroup_iter, one needs to set a cgroup to the iter_link > created from attaching. This cgroup is passed as a file descriptor and > serves as the starting point of the walk. > > For walking descendants, one can specify the order: either pre-order or > post-order. For walking ancestors, the walk starts at the specified > cgroup and ends at the root. > > 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 based off a patch in the mailing > list which adds a new kfunc set for sleepable functions: > "btf: Add a new kfunc set which allows to mark a function to be > sleepable" [1]. > > Patches in this series are organized as follows: > * Patch 1 enables the use of cgroup_get_from_file() in cgroup1. > This is useful because it enables cgroup_iter to work with cgroup1, and > allows the entire stat collection workflow to be cgroup1-compatible. > * Patches 2-5 introduce cgroup_iter prog, and a selftest. > * Patches 6-8 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. > > v1 -> v2: > - Redesign of cgroup_iter from v1, based on Alexei's idea [2]: > - supports walking cgroup subtree. > - supports walking ancestors of a cgroup. (Andrii) > - supports terminating the walk early. > - uses fd instead of cgroup_id as parameter for iter_link. Using fd is > a convention in bpf. > - gets cgroup's ref at attach time and deref at detach. > - brought back cgroup1 support for cgroup_iter. > - Squashed the patches adding the rstat flush hook points and kfuncs > (Tejun). > - Added a comment explaining why bpf_rstat_flush() needs to be weak > (Tejun). > - Updated the final selftest with the new cgroup_iter design. > - Changed CHECKs in the selftest with ASSERTs (Yonghong, Andrii). > - Removed empty line at the end of the selftest (Yonghong). > - Renamed test files to cgroup_hierarchical_stats.c. > - Reordered CGROUP_PATH params order to match struct declaration > in the selftest (Michal). > - Removed memory_subsys_enabled() and made sure memcg controller > enablement checks make sense and are documented (Michal). > > RFC v2 -> v1: > - Instead of introducing a new program type for rstat flushing, add an > empty hook point, bpf_rstat_flush(), and use fentry bpf programs to > attach to it and flush bpf stats. > - Instead of using helpers, use kfuncs for rstat functions. > - These changes simplify the patchset greatly, with minimal changes to > uapi. > > RFC v1 -> RFC v2: > - Instead of rstat flush programs attach to subsystems, they now attach > to rstat (global flushers, not per-subsystem), based on discussions > with Tejun. The first patch is entirely rewritten. > - Pass cgroup pointers to rstat flushers instead of cgroup ids. This is > much more flexibility and less likely to need a uapi update later. > - rstat helpers are now only defined if CGROUP_CONFIG. > - Most of the code is now only defined if CGROUP_CONFIG and > CONFIG_BPF_SYSCALL. > - Move rstat helper protos from bpf_base_func_proto() to > tracing_prog_func_proto(). > - rstat helpers argument (cgroup pointer) is now ARG_PTR_TO_BTF_ID, not > ARG_ANYTHING. > - Rewrote the selftest to use the cgroup helpers. > - Dropped bpf_map_lookup_percpu_elem (already added by Feng). > - Dropped patch to support cgroup v1 for cgroup_iter. > - Dropped patch to define some cgroup_put() when !CONFIG_CGROUP. The > code that calls it is no longer compiled when !CONFIG_CGROUP. > > cgroup_iter was originally introduced in a different patch series[3]. > Hao and I agreed that it fits better as part of this series. > RFC v1 of this patch series had the following changes from [3]: > - Getting the cgroup's reference at the time at attaching, instead of > at the time when iterating. (Yonghong) > - Remove .init_seq_private and .fini_seq_private callbacks for > cgroup_iter. They are not needed now. (Yonghong) > > [1] https://lore.kernel.org/bpf/20220421140740.459558-5-benjamin.tissoires@xxxxxxxxxx/ > [2] https://lore.kernel.org/bpf/20220520221919.jnqgv52k4ajlgzcl@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ > [3] https://lore.kernel.org/lkml/20220225234339.2386398-9-haoluo@xxxxxxxxxx/ > > Hao Luo (4): > cgroup: Add cgroup_put() in !CONFIG_CGROUPS case > bpf, iter: Fix the condition on p when calling stop. > bpf: Introduce cgroup iter > selftests/bpf: Test cgroup_iter. > > Yosry Ahmed (4): > cgroup: enable cgroup_get_from_file() on cgroup1 > cgroup: bpf: enable bpf programs to integrate with rstat > selftests/bpf: extend cgroup helpers > bpf: add a selftest for cgroup hierarchical stats collection > > include/linux/bpf.h | 8 + > include/linux/cgroup.h | 3 + > include/uapi/linux/bpf.h | 21 ++ > kernel/bpf/Makefile | 2 +- > kernel/bpf/bpf_iter.c | 5 + > kernel/bpf/cgroup_iter.c | 235 ++++++++++++ > kernel/cgroup/cgroup.c | 5 - > kernel/cgroup/rstat.c | 46 +++ > tools/include/uapi/linux/bpf.h | 21 ++ > tools/testing/selftests/bpf/cgroup_helpers.c | 173 +++++++-- > tools/testing/selftests/bpf/cgroup_helpers.h | 15 +- > .../prog_tests/cgroup_hierarchical_stats.c | 351 ++++++++++++++++++ > .../selftests/bpf/prog_tests/cgroup_iter.c | 190 ++++++++++ > tools/testing/selftests/bpf/progs/bpf_iter.h | 7 + > .../bpf/progs/cgroup_hierarchical_stats.c | 234 ++++++++++++ > .../testing/selftests/bpf/progs/cgroup_iter.c | 39 ++ > 16 files changed, 1303 insertions(+), 52 deletions(-) > create mode 100644 kernel/bpf/cgroup_iter.c > create mode 100644 tools/testing/selftests/bpf/prog_tests/cgroup_hierarchical_stats.c > create mode 100644 tools/testing/selftests/bpf/prog_tests/cgroup_iter.c > create mode 100644 tools/testing/selftests/bpf/progs/cgroup_hierarchical_stats.c > create mode 100644 tools/testing/selftests/bpf/progs/cgroup_iter.c > > -- > 2.36.1.476.g0c4daa206d-goog >
