Messages in this thread | | | Date | Fri, 1 Jul 2022 17:55:10 -0700 | Subject | Re: [PATCH bpf-next v2 8/8] bpf: add a selftest for cgroup hierarchical stats collection | From | Yonghong Song <> |
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On 6/29/22 1:04 AM, Yosry Ahmed wrote: > On Tue, Jun 28, 2022 at 11:48 PM Yonghong Song <yhs@fb.com> wrote: >> >> >> >> On 6/28/22 5:09 PM, Yosry Ahmed wrote: >>> On Tue, Jun 28, 2022 at 12:14 AM Yosry Ahmed <yosryahmed@google.com> wrote: >>>> >>>> On Mon, Jun 27, 2022 at 11:47 PM Yosry Ahmed <yosryahmed@google.com> wrote: >>>>> >>>>> On Mon, Jun 27, 2022 at 11:14 PM Yonghong Song <yhs@fb.com> wrote: >>>>>> >>>>>> >>>>>> >>>>>> On 6/10/22 12:44 PM, Yosry Ahmed wrote: >>>>>>> Add a selftest that tests the whole workflow for collecting, >>>>>>> aggregating (flushing), and displaying cgroup hierarchical stats. >>>>>>> >>>>>>> TL;DR: >>>>>>> - 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. >>>>>>> >>>>>>> Detailed explanation: >>>>>>> - The test loads tracing bpf programs, vmscan_start and vmscan_end, to >>>>>>> measure the latency of cgroup reclaim. Per-cgroup ratings 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). >>>>>>> >>>>>>> Signed-off-by: Yosry Ahmed <yosryahmed@google.com> >>>>>> >>>>>> There are a selftest failure with test: >>>>>> >>>>>> get_cgroup_vmscan_delay:PASS:output format 0 nsec >>>>>> get_cgroup_vmscan_delay:PASS:cgroup_id 0 nsec >>>>>> get_cgroup_vmscan_delay:PASS:vmscan_reading 0 nsec >>>>>> get_cgroup_vmscan_delay:PASS:read cgroup_iter 0 nsec >>>>>> get_cgroup_vmscan_delay:PASS:output format 0 nsec >>>>>> 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 >>>>>> 781874 != expected 382092 >>>>>> check_vmscan_stats:FAIL:child2_vmscan unexpected child2_vmscan: actual >>>>>> -1 != expected -2 >>>>>> check_vmscan_stats:FAIL:test_vmscan unexpected test_vmscan: actual >>>>>> 781874 != expected 781873 >>>>>> check_vmscan_stats:FAIL:root_vmscan unexpected root_vmscan: actual 0 < >>>>>> expected 781874 >>>>>> destroy_progs:PASS:remove cgroup_iter pin 0 nsec >>>>>> destroy_progs:PASS:remove cgroup_iter pin 0 nsec >>>>>> destroy_progs:PASS:remove cgroup_iter pin 0 nsec >>>>>> destroy_progs:PASS:remove cgroup_iter pin 0 nsec >>>>>> destroy_progs:PASS:remove cgroup_iter pin 0 nsec >>>>>> destroy_progs:PASS:remove cgroup_iter pin 0 nsec >>>>>> destroy_progs:PASS:remove cgroup_iter pin 0 nsec >>>>>> destroy_progs:PASS:remove cgroup_iter root pin 0 nsec >>>>>> cleanup_bpffs:PASS:rmdir /sys/fs/bpf/vmscan/ 0 nsec >>>>>> #33 cgroup_hierarchical_stats:FAIL >>>>>> >>>>> >>>>> The test is passing on my setup. I am trying to figure out if there is >>>>> something outside the setup done by the test that can cause the test >>>>> to fail. >>>>> >>>> >>>> I can't reproduce the failure on my machine. It seems like for some >>>> reason reclaim is not invoked in one of the test cgroups which results >>>> in the expected stats not being there. I have a few suspicions as to >>>> what might cause this but I am not sure. >>>> >>>> If you have the capacity, do you mind re-running the test with the >>>> attached diff1.patch? (and maybe diff2.patch if that fails, this will >>>> cause OOMs in the test cgroup, you might see some process killed >>>> warnings). >>>> Thanks! >>>> >>> >>> In addition to that, it looks like one of the cgroups has a "0" stat >>> which shouldn't happen unless one of the map update/lookup operations >>> failed, which should log something using bpf_printk. I need to >>> reproduce the test failure to investigate this properly. Did you >>> observe this failure on your machine or in CI? Any instructions on how >>> to reproduce or system setup? >> >> I got "0" as well. >> >> get_cgroup_vmscan_delay:FAIL:vmscan_reading unexpected vmscan_reading: >> actual 0 <= expected 0 >> check_vmscan_stats:FAIL:child1_vmscan unexpected child1_vmscan: actual >> 676612 != expected 339142 >> check_vmscan_stats:FAIL:child2_vmscan unexpected child2_vmscan: actual >> -1 != expected -2 >> check_vmscan_stats:FAIL:test_vmscan unexpected test_vmscan: actual >> 676612 != expected 676611 >> check_vmscan_stats:FAIL:root_vmscan unexpected root_vmscan: actual 0 < >> expected 676612 >> >> I don't have special config. I am running on qemu vm, similar to >> ci environment but may have a slightly different config. >> >> The CI for this patch set won't work since the sleepable kfunc support >> patch is not available. Once you have that patch, bpf CI should be able >> to compile the patch set and run the tests. >> > > I will include this patch in the next version anyway, but I am trying > to find out why this selftest is failing for you before I send it out. > I am trying to reproduce the problem but no luck so far.
I debugged this a little bit and found that this two programs
SEC("tp_btf/mm_vmscan_memcg_reclaim_begin") int BPF_PROG(vmscan_start, struct lruvec *lruvec, struct scan_control *sc)
and
SEC("tp_btf/mm_vmscan_memcg_reclaim_end") int BPF_PROG(vmscan_end, struct lruvec *lruvec, struct scan_control *sc)
are not triggered.
I do have CONFIG_MEMCG enabled in my config file: ... CONFIG_MEMCG=y CONFIG_MEMCG_SWAP=y CONFIG_MEMCG_KMEM=y ...
Maybe when cgroup_rstat_flush() is called, some code path won't trigger mm_vmscan_memcg_reclaim_begin/end()?
> >>> >>>> >>>>>> >>>>>> Also an existing test also failed. >>>>>> >>>>>> btf_dump_data:PASS:find type id 0 nsec >>>>>> >>>>>> >>>>>> btf_dump_data:PASS:failed/unexpected type_sz 0 nsec >>>>>> >>>>>> >>>>>> btf_dump_data:FAIL:ensure expected/actual match unexpected ensure >>>>>> expected/actual match: actual '(union bpf_iter_link_info){.map = >>>>>> (struct){.map_fd = (__u32)1,},.cgroup ' >>>>>> test_btf_dump_struct_data:PASS:find struct sk_buff 0 nsec >>>>>> >>>>> >>>>> Yeah I see what happened there. bpf_iter_link_info was changed by the >>>>> patch that introduced cgroup_iter, and this specific union is used by >>>>> the test to test the "union with nested struct" btf dumping. I will >>>>> add a patch in the next version that updates the btf_dump_data test >>>>> accordingly. Thanks. >>>>> >>>>>> >>>>>> test_btf_dump_struct_data:PASS:unexpected return value dumping sk_buff 0 >>>>>> nsec >>>>>> >>>>>> btf_dump_data:PASS:verify prefix match 0 nsec >>>>>> >>>>>> >>>>>> btf_dump_data:PASS:find type id 0 nsec >>>>>> >>>>>> >>>>>> btf_dump_data:PASS:failed to return -E2BIG 0 nsec >>>>>> >>>>>> >>>>>> btf_dump_data:PASS:ensure expected/actual match 0 nsec >>>>>> >>>>>> >>>>>> btf_dump_data:PASS:verify prefix match 0 nsec >>>>>> >>>>>> >>>>>> btf_dump_data:PASS:find type id 0 nsec >>>>>> >>>>>> >>>>>> btf_dump_data:PASS:failed to return -E2BIG 0 nsec >>>>>> >>>>>> >>>>>> btf_dump_data:PASS:ensure expected/actual match 0 nsec >>>>>> >>>>>> >>>>>> #21/14 btf_dump/btf_dump: struct_data:FAIL >>>>>> >>>>>> please take a look. >>>>>> >>>>>>> --- >>>>>>> .../prog_tests/cgroup_hierarchical_stats.c | 351 ++++++++++++++++++ >>>>>>> .../bpf/progs/cgroup_hierarchical_stats.c | 234 ++++++++++++ >>>>>>> 2 files changed, 585 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 >>>>>>> >> [...]
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