[bpf-next,v2,0/4] introduce bpf_strncmp() helper

Message

Hou Tao Dec. 10, 2021, 2:16 p.m. UTC

Hi,

The motivation for introducing bpf_strncmp() helper comes from
two aspects:

(1) clang doesn't always replace strncmp() automatically
In tracing program, sometimes we need to using a home-made
strncmp() to check whether or not the file name is expected.

(2) the performance of home-made strncmp is not so good
As shown in the benchmark in patch #4, the performance of
bpf_strncmp() helper is 18% or 33% better than home-made strncmp()
under x86-64 or arm64 when the compared string length is 64. When
the string length grows to 4095, the performance win will be
179% or 600% under x86-64 or arm64.

Any comments are welcome.
Regards,
Tao

Change Log:
v2:
 * rebased on bpf-next
 * drop patch "selftests/bpf: factor out common helpers for benchmarks"
   (suggested by Andrii)
 * remove unnecessary inline functions and add comments for programs which
   will be rejected by verifier in patch 4 (suggested by Andrii)
 * rename variables used in will-fail programs to clarify the purposes.

v1: https://lore.kernel.org/bpf/[e-mail]
 * change API to bpf_strncmp(const char *s1, u32 s1_sz, const char *s2)
 * add benchmark refactor and benchmark between bpf_strncmp() and strncmp()

RFC: https://lore.kernel.org/bpf/[e-mail]/

Hou Tao (4):
  bpf: add bpf_strncmp helper
  selftests/bpf: fix checkpatch error on empty function parameter
  selftests/bpf: add benchmark for bpf_strncmp() helper
  selftests/bpf: add test cases for bpf_strncmp()

 include/linux/bpf.h                           |   1 +
 include/uapi/linux/bpf.h                      |  11 ++
 kernel/bpf/helpers.c                          |  16 ++
 tools/include/uapi/linux/bpf.h                |  11 ++
 tools/testing/selftests/bpf/Makefile          |   4 +-
 tools/testing/selftests/bpf/bench.c           |   8 +-
 tools/testing/selftests/bpf/bench.h           |   9 +-
 .../selftests/bpf/benchs/bench_count.c        |   2 +-
 .../selftests/bpf/benchs/bench_rename.c       |  16 +-
 .../selftests/bpf/benchs/bench_ringbufs.c     |  14 +-
 .../selftests/bpf/benchs/bench_strncmp.c      | 161 +++++++++++++++++
 .../selftests/bpf/benchs/bench_trigger.c      |  24 +--
 .../selftests/bpf/benchs/run_bench_strncmp.sh |  12 ++
 .../selftests/bpf/prog_tests/test_strncmp.c   | 167 ++++++++++++++++++
 .../selftests/bpf/progs/strncmp_bench.c       |  50 ++++++
 .../selftests/bpf/progs/strncmp_test.c        |  54 ++++++
 16 files changed, 526 insertions(+), 34 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/benchs/bench_strncmp.c
 create mode 100755 tools/testing/selftests/bpf/benchs/run_bench_strncmp.sh
 create mode 100644 tools/testing/selftests/bpf/prog_tests/test_strncmp.c
 create mode 100644 tools/testing/selftests/bpf/progs/strncmp_bench.c
 create mode 100644 tools/testing/selftests/bpf/progs/strncmp_test.c

Comments

Alexei Starovoitov Dec. 12, 2021, 1:50 a.m. UTC | #1

On Fri, Dec 10, 2021 at 6:01 AM Hou Tao <[e-mail]> wrote:
>
> Hi,
>
> The motivation for introducing bpf_strncmp() helper comes from
> two aspects:
>
> (1) clang doesn't always replace strncmp() automatically
> In tracing program, sometimes we need to using a home-made
> strncmp() to check whether or not the file name is expected.
>
> (2) the performance of home-made strncmp is not so good
> As shown in the benchmark in patch #4, the performance of
> bpf_strncmp() helper is 18% or 33% better than home-made strncmp()
> under x86-64 or arm64 when the compared string length is 64. When
> the string length grows to 4095, the performance win will be
> 179% or 600% under x86-64 or arm64.
>
> Any comments are welcome.
> Regards,
> Tao
>
> Change Log:
> v2:
>  * rebased on bpf-next
>  * drop patch "selftests/bpf: factor out common helpers for benchmarks"
>    (suggested by Andrii)
>  * remove unnecessary inline functions and add comments for programs which
>    will be rejected by verifier in patch 4 (suggested by Andrii)
>  * rename variables used in will-fail programs to clarify the purposes.

Applied. Thanks