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  1. 16 5月, 2020 11 次提交
  3. 15 5月, 2020 15 次提交
  5. 14 5月, 2020 6 次提交
    • Y
      bpf: Change btf_iter func proto prefix to "bpf_iter_" · 21aef70e
      由 Yonghong Song 提交于 
      This is to be consistent with tracing and lsm programs
which have prefix "bpf_trace_" and "bpf_lsm_" respectively.
Suggested-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NYonghong Song <yhs@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NAndrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200513180216.2949387-1-yhs@fb.com
      21aef70e
    • Y
      tools/bpf: selftests : Explain bpf_iter test failures with llvm 10.0.0 · 99aaf53e
      由 Yonghong Song 提交于 
      Commit 6879c042 ("tools/bpf: selftests: Add bpf_iter selftests")
added self tests for bpf_iter feature. But two subtests
ipv6_route and netlink needs llvm latest 10.x release branch
or trunk due to a bug in llvm BPF backend. This patch added
the file README.rst to document these two failures
so people using llvm 10.0.0 can be aware of them.
Suggested-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NYonghong Song <yhs@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200513180215.2949237-1-yhs@fb.com
      99aaf53e
    • A
      selftest/bpf: Add BPF triggering benchmark · c5d420c3
      由 Andrii Nakryiko 提交于 
      It is sometimes desirable to be able to trigger BPF program from user-space
with minimal overhead. sys_enter would seem to be a good candidate, yet in
a lot of cases there will be a lot of noise from syscalls triggered by other
processes on the system. So while searching for low-overhead alternative, I've
stumbled upon getpgid() syscall, which seems to be specific enough to not
suffer from accidental syscall by other apps.

This set of benchmarks compares tp, raw_tp w/ filtering by syscall ID, kprobe,
fentry and fmod_ret with returning error (so that syscall would not be
executed), to determine the lowest-overhead way. Here are results on my
machine (using benchs/run_bench_trigger.sh script):

  base      :    9.200 ± 0.319M/s
  tp        :    6.690 ± 0.125M/s
  rawtp     :    8.571 ± 0.214M/s
  kprobe    :    6.431 ± 0.048M/s
  fentry    :    8.955 ± 0.241M/s
  fmodret   :    8.903 ± 0.135M/s

So it seems like fmodret doesn't give much benefit for such lightweight
syscall. Raw tracepoint is pretty decent despite additional filtering logic,
but it will be called for any other syscall in the system, which rules it out.
Fentry, though, seems to be adding the least amoung of overhead and achieves
97.3% of performance of baseline no-BPF-attached syscall.

Using getpgid() seems to be preferable to set_task_comm() approach from
test_overhead, as it's about 2.35x faster in a baseline performance.
Signed-off-by: NAndrii Nakryiko <andriin@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NJohn Fastabend <john.fastabend@gmail.com>
Acked-by: NYonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200512192445.2351848-5-andriin@fb.com
      c5d420c3
    • A
      selftest/bpf: Fmod_ret prog and implement test_overhead as part of bench · 4eaf0b5c
      由 Andrii Nakryiko 提交于 
      Add fmod_ret BPF program to existing test_overhead selftest. Also re-implement
user-space benchmarking part into benchmark runner to compare results. Results
with ./bench are consistently somewhat lower than test_overhead's, but relative
performance of various types of BPF programs stay consisten (e.g., kretprobe is
noticeably slower). This slowdown seems to be coming from the fact that
test_overhead is single-threaded, while benchmark always spins off at least
one thread for producer. This has been confirmed by hacking multi-threaded
test_overhead variant and also single-threaded bench variant. Resutls are
below. run_bench_rename.sh script from benchs/ subdirectory was used to
produce results for ./bench.

Single-threaded implementations
===============================

/* bench: single-threaded, atomics */
base      :    4.622 ± 0.049M/s
kprobe    :    3.673 ± 0.052M/s
kretprobe :    2.625 ± 0.052M/s
rawtp     :    4.369 ± 0.089M/s
fentry    :    4.201 ± 0.558M/s
fexit     :    4.309 ± 0.148M/s
fmodret   :    4.314 ± 0.203M/s

/* selftest: single-threaded, no atomics */
task_rename base        4555K events per sec
task_rename kprobe      3643K events per sec
task_rename kretprobe   2506K events per sec
task_rename raw_tp      4303K events per sec
task_rename fentry      4307K events per sec
task_rename fexit       4010K events per sec
task_rename fmod_ret    3984K events per sec

Multi-threaded implementations
==============================

/* bench: multi-threaded w/ atomics */
base      :    3.910 ± 0.023M/s
kprobe    :    3.048 ± 0.037M/s
kretprobe :    2.300 ± 0.015M/s
rawtp     :    3.687 ± 0.034M/s
fentry    :    3.740 ± 0.087M/s
fexit     :    3.510 ± 0.009M/s
fmodret   :    3.485 ± 0.050M/s

/* selftest: multi-threaded w/ atomics */
task_rename base        3872K events per sec
task_rename kprobe      3068K events per sec
task_rename kretprobe   2350K events per sec
task_rename raw_tp      3731K events per sec
task_rename fentry      3639K events per sec
task_rename fexit       3558K events per sec
task_rename fmod_ret    3511K events per sec

/* selftest: multi-threaded, no atomics */
task_rename base        3945K events per sec
task_rename kprobe      3298K events per sec
task_rename kretprobe   2451K events per sec
task_rename raw_tp      3718K events per sec
task_rename fentry      3782K events per sec
task_rename fexit       3543K events per sec
task_rename fmod_ret    3526K events per sec

Note that the fact that ./bench benchmark always uses atomic increments for
counting, while test_overhead doesn't, doesn't influence test results all that
much.
Signed-off-by: NAndrii Nakryiko <andriin@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NJohn Fastabend <john.fastabend@gmail.com>
Acked-by: NYonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200512192445.2351848-4-andriin@fb.com
      4eaf0b5c
    • A
      selftests/bpf: Add benchmark runner infrastructure · 8e7c2a02
      由 Andrii Nakryiko 提交于 
      While working on BPF ringbuf implementation, testing, and benchmarking, I've
developed a pretty generic and modular benchmark runner, which seems to be
generically useful, as I've already used it for one more purpose (testing
fastest way to trigger BPF program, to minimize overhead of in-kernel code).

This patch adds generic part of benchmark runner and sets up Makefile for
extending it with more sets of benchmarks.

Benchmarker itself operates by spinning up specified number of producer and
consumer threads, setting up interval timer sending SIGALARM signal to
application once a second. Every second, current snapshot with hits/drops
counters are collected and stored in an array. Drops are useful for
producer/consumer benchmarks in which producer might overwhelm consumers.

Once test finishes after given amount of warm-up and testing seconds, mean and
stddev are calculated (ignoring warm-up results) and is printed out to stdout.
This setup seems to give consistent and accurate results.

To validate behavior, I added two atomic counting tests: global and local.
For global one, all the producer threads are atomically incrementing same
counter as fast as possible. This, of course, leads to huge drop of
performance once there is more than one producer thread due to CPUs fighting
for the same memory location.

Local counting, on the other hand, maintains one counter per each producer
thread, incremented independently. Once per second, all counters are read and
added together to form final "counting throughput" measurement. As expected,
such setup demonstrates linear scalability with number of producers (as long
as there are enough physical CPU cores, of course). See example output below.
Also, this setup can nicely demonstrate disastrous effects of false sharing,
if care is not taken to take those per-producer counters apart into
independent cache lines.

Demo output shows global counter first with 1 producer, then with 4. Both
total and per-producer performance significantly drop. The last run is local
counter with 4 producers, demonstrating near-perfect scalability.

$ ./bench -a -w1 -d2 -p1 count-global
Setting up benchmark 'count-global'...
Benchmark 'count-global' started.
Iter   0 ( 24.822us): hits  148.179M/s (148.179M/prod), drops    0.000M/s
Iter   1 ( 37.939us): hits  149.308M/s (149.308M/prod), drops    0.000M/s
Iter   2 (-10.774us): hits  150.717M/s (150.717M/prod), drops    0.000M/s
Iter   3 (  3.807us): hits  151.435M/s (151.435M/prod), drops    0.000M/s
Summary: hits  150.488 ± 1.079M/s (150.488M/prod), drops    0.000 ± 0.000M/s

$ ./bench -a -w1 -d2 -p4 count-global
Setting up benchmark 'count-global'...
Benchmark 'count-global' started.
Iter   0 ( 60.659us): hits   53.910M/s ( 13.477M/prod), drops    0.000M/s
Iter   1 (-17.658us): hits   53.722M/s ( 13.431M/prod), drops    0.000M/s
Iter   2 (  5.865us): hits   53.495M/s ( 13.374M/prod), drops    0.000M/s
Iter   3 (  0.104us): hits   53.606M/s ( 13.402M/prod), drops    0.000M/s
Summary: hits   53.608 ± 0.113M/s ( 13.402M/prod), drops    0.000 ± 0.000M/s

$ ./bench -a -w1 -d2 -p4 count-local
Setting up benchmark 'count-local'...
Benchmark 'count-local' started.
Iter   0 ( 23.388us): hits  640.450M/s (160.113M/prod), drops    0.000M/s
Iter   1 (  2.291us): hits  605.661M/s (151.415M/prod), drops    0.000M/s
Iter   2 ( -6.415us): hits  607.092M/s (151.773M/prod), drops    0.000M/s
Iter   3 ( -1.361us): hits  601.796M/s (150.449M/prod), drops    0.000M/s
Summary: hits  604.849 ± 2.739M/s (151.212M/prod), drops    0.000 ± 0.000M/s

Benchmark runner supports setting thread affinity for producer and consumer
threads. You can use -a flag for default CPU selection scheme, where first
consumer gets CPU #0, next one gets CPU #1, and so on. Then producer threads
pick up next CPU and increment one-by-one as well. But user can also specify
a set of CPUs independently for producers and consumers with --prod-affinity
1,2-10,15 and --cons-affinity <set-of-cpus>. The latter allows to force
producers and consumers to share same set of CPUs, if necessary.
Signed-off-by: NAndrii Nakryiko <andriin@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NYonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200512192445.2351848-3-andriin@fb.com
      8e7c2a02
    • A
      selftests/bpf: Extract parse_num_list into generic testing_helpers.c · cd49291c
      由 Andrii Nakryiko 提交于 
      Add testing_helpers.c, which will contain generic helpers for test runners and
tests needing some common generic functionality, like parsing a set of
numbers.
Signed-off-by: NAndrii Nakryiko <andriin@fb.com>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NYonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200512192445.2351848-2-andriin@fb.com
      cd49291c
  7. 13 5月, 2020 2 次提交
  9. 12 5月, 2020 4 次提交
  11. 11 5月, 2020 1 次提交
    • G
      bpf, libbpf: Replace zero-length array with flexible-array · 385bbf7b
      由 Gustavo A. R. Silva 提交于 
      The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

sizeof(flexible-array-member) triggers a warning because flexible array
members have incomplete type[1]. There are some instances of code in
which the sizeof operator is being incorrectly/erroneously applied to
zero-length arrays and the result is zero. Such instances may be hiding
some bugs. So, this work (flexible-array member conversions) will also
help to get completely rid of those sorts of issues.

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: NGustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NYonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200507185057.GA13981@embeddedor
      385bbf7b
  13. 10 5月, 2020 1 次提交