From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yonghong Song Subject: Re: [PATCH bpf-next v2 8/8] bpf: add a selftest for cgroup hierarchical stats collection Date: Tue, 28 Jun 2022 23:26:51 -0700 Message-ID: <59376285-21bc-ff12-3d64-3ea7257becb2@fb.com> References: <20220610194435.2268290-1-yosryahmed@google.com> <20220610194435.2268290-9-yosryahmed@google.com> <00df1932-38fe-c6f8-49d0-3a44affb1268@fb.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=message-id : date : subject : to : cc : references : from : in-reply-to : content-type : content-transfer-encoding : mime-version; s=facebook; bh=A/sEaSIpioHKs2Bbfr4HKimR0DcmMDLF9iK8j7qY+eY=; b=Ww9LpyYmmYKTi3My2zLD3ESJKjaAoFOU+865EhcOpMfUMhvJ9TqikzC+9esTiFbjyjg+ 3AKzhzja8+V0SoSek+6/4TBRbYvb5y1re2wbSVFgWbqLDn0K7Vdk+JG9h5uR8+w1LW6d 2pgyLQ9DBakkNts+kLe3HfIUaDQ02WBAsXo= Content-Language: en-US In-Reply-To: List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Yosry Ahmed Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Song Liu , John Fastabend , KP Singh , Hao Luo , Tejun Heo , Zefan Li , Johannes Weiner , Shuah Khan , Michal Hocko , Roman Gushchin , David Rientjes , Stanislav Fomichev , Greg Thelen , Shakeel Butt , Linux Kernel Mailing List , Networking , bpf On 6/28/22 12:43 AM, Yosry Ahmed wrote: > On Mon, Jun 27, 2022 at 11:47 PM Yosry Ahmed wrote: >> >> On Mon, Jun 27, 2022 at 11:14 PM Yonghong Song 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 >>> >>> 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. >> >>> >>> 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. >> > > So I actually tried the attached diff to updated the expected dump of > bpf_iter_link_info in this test, but the test still failed: > > 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 = (struct){.cgroup_fd = > (__u32)1,},}' != expected '(union bpf_iter_link_info){.map = > (struct){.map_fd = (__u32)1,},.cgroup = (struct){.cgroup_fd = > (__u32)1,.traversal_order = (__u32)1},}' > > It seems to me that the actual output in this case is not right, it is > missing traversal_order. Did we accidentally find a bug in btf dumping > of unions with nested structs, or am I missing something here? Probably there is an issue in btf_dump_data() function in tools/lib/bpf/btf_dump.c. Could you take a look at it? > 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 >>>> [...]