Messages in this thread | | | Date | Tue, 28 Jun 2022 23:17:16 -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 6/28/22 12:14 AM, Yosry Ahmed 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).
The patch doesn't help. Still failed.
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 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 destroy_progs:PASS:remove cgroup_iter pin 0 nsec destroy_progs:PASS:remove cgroup_iter pin 0 nsec
> Thanks! > > >>> >>> Also an existing test also failed. [...]
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