Messages in this thread | | | Date | Sun, 10 Jul 2022 17:26:21 -0700 | Subject | Re: [PATCH bpf-next v3 8/8] bpf: add a selftest for cgroup hierarchical stats collection | From | Yonghong Song <> |
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On 7/8/22 5:04 PM, 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> > --- > .../prog_tests/cgroup_hierarchical_stats.c | 362 ++++++++++++++++++ > .../bpf/progs/cgroup_hierarchical_stats.c | 235 ++++++++++++ > 2 files changed, 597 insertions(+) > create mode 100644 tools/testing/selftests/bpf/prog_tests/cgroup_hierarchical_stats.c > create mode 100644 tools/testing/selftests/bpf/progs/cgroup_hierarchical_stats.c > [...] > + > +static unsigned long long get_cgroup_vmscan_delay(unsigned long long cgroup_id, > + const char *file_name) > +{ > + char buf[128], path[128]; > + unsigned long long vmscan = 0, id = 0; > + int err; > + > + /* For every cgroup, read the file generated by cgroup_iter */ > + snprintf(path, 128, "%s%s", BPFFS_VMSCAN, file_name); > + err = read_from_file(path, buf, 128); > + if (!ASSERT_OK(err, "read cgroup_iter")) > + return 0; > + > + /* Check the output file formatting */ > + ASSERT_EQ(sscanf(buf, "cg_id: %llu, total_vmscan_delay: %llu\n", > + &id, &vmscan), 2, "output format"); > + > + /* Check that the cgroup_id is displayed correctly */ > + ASSERT_EQ(id, cgroup_id, "cgroup_id"); > + /* Check that the vmscan reading is non-zero */ > + ASSERT_GT(vmscan, 0, "vmscan_reading"); > + return vmscan; > +} > + > +static void check_vmscan_stats(void) > +{ > + int i; > + unsigned long long vmscan_readings[N_CGROUPS], vmscan_root; > + > + for (i = 0; i < N_CGROUPS; i++) > + vmscan_readings[i] = get_cgroup_vmscan_delay(cgroups[i].id, > + cgroups[i].name); > + > + /* Read stats for root too */ > + vmscan_root = get_cgroup_vmscan_delay(CG_ROOT_ID, CG_ROOT_NAME); > + > + /* Check that child1 == child1_1 + child1_2 */ > + ASSERT_EQ(vmscan_readings[1], vmscan_readings[3] + vmscan_readings[4], > + "child1_vmscan"); > + /* Check that child2 == child2_1 + child2_2 */ > + ASSERT_EQ(vmscan_readings[2], vmscan_readings[5] + vmscan_readings[6], > + "child2_vmscan"); > + /* Check that test == child1 + child2 */ > + ASSERT_EQ(vmscan_readings[0], vmscan_readings[1] + vmscan_readings[2], > + "test_vmscan"); > + /* Check that root >= test */ > + ASSERT_GE(vmscan_root, vmscan_readings[1], "root_vmscan");
I still get a test failure with
get_cgroup_vmscan_delay:PASS:cgroup_id 0 nsec get_cgroup_vmscan_delay:FAIL:vmscan_reading unexpected vmscan_reading: actual 0 <= expected 0 check_vmscan_stats:FAIL:child1_vmscan unexpected child1_vmscan: actual 0 != expected -2 check_vmscan_stats:FAIL:child2_vmscan unexpected child2_vmscan: actual 0 != expected -2 check_vmscan_stats:PASS:test_vmscan 0 nsec check_vmscan_stats:PASS:root_vmscan 0 nsec
I added 'dump_stack()' in function try_to_free_mem_cgroup_pages() and run this test (#33) and didn't get any stacktrace. But I do get stacktraces due to other operations like try_to_free_mem_cgroup_pages+0x1fd [kernel] try_to_free_mem_cgroup_pages+0x1fd [kernel] memory_reclaim_write+0x88 [kernel] cgroup_file_write+0x88 [kernel] kernfs_fop_write_iter+0xd0 [kernel] vfs_write+0x2c4 [kernel] __x64_sys_write+0x60 [kernel] do_syscall_64+0x2d [kernel] entry_SYSCALL_64_after_hwframe+0x44 [kernel]
If you can show me the stacktrace about how try_to_free_mem_cgroup_pages() is triggered in your setup, I can help debug this problem in my environment.
> +} > + > +static int setup_cgroup_iter(struct cgroup_hierarchical_stats *obj, int cgroup_fd, [...]
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