Re: [PATCH v2 bpf-next 2/3] selftest/bpf: fmod_ret prog and implement test_overhead as part of bench

[Yonghong Song <yhs@fb.com>]

On 5/8/20 4:20 PM, Andrii Nakryiko wrote:
> 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).
> 
> run_bench_rename.sh script (in benchs/ directory) was used to produce the
> following numbers:
> 
>    base      :    3.975 ± 0.065M/s
>    kprobe    :    3.268 ± 0.095M/s
>    kretprobe :    2.496 ± 0.040M/s
>    rawtp     :    3.899 ± 0.078M/s
>    fentry    :    3.836 ± 0.049M/s
>    fexit     :    3.660 ± 0.082M/s
>    fmodret   :    3.776 ± 0.033M/s
> 
> While running test_overhead gives:
> 
>    task_rename base        4457K events per sec
>    task_rename kprobe      3849K events per sec
>    task_rename kretprobe   2729K events per sec
>    task_rename raw_tp      4506K events per sec
>    task_rename fentry      4381K events per sec
>    task_rename fexit       4349K events per sec
>    task_rename fmod_ret    4130K events per sec

Do you where the overhead is and how we could provide options in
bench to reduce the overhead so we can achieve similar numbers?
For benchmarking, sometimes you really want to see "true"
potential of a particular implementation.

> 
> Acked-by: John Fastabend <john.fastabend@gmail.com>
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>
> ---
>   tools/testing/selftests/bpf/Makefile          |   4 +-
>   tools/testing/selftests/bpf/bench.c           |  14 ++
>   .../selftests/bpf/benchs/bench_rename.c       | 195 ++++++++++++++++++
>   .../selftests/bpf/benchs/run_bench_rename.sh  |   9 +
>   .../selftests/bpf/prog_tests/test_overhead.c  |  14 +-
>   .../selftests/bpf/progs/test_overhead.c       |   6 +
>   6 files changed, 240 insertions(+), 2 deletions(-)
>   create mode 100644 tools/testing/selftests/bpf/benchs/bench_rename.c
>   create mode 100755 tools/testing/selftests/bpf/benchs/run_bench_rename.sh
> 
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index 289fffbf975e..29a02abf81a3 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -409,10 +409,12 @@ $(OUTPUT)/test_cpp: test_cpp.cpp $(OUTPUT)/test_core_extern.skel.h $(BPFOBJ)
>   $(OUTPUT)/bench_%.o: benchs/bench_%.c bench.h
>   	$(call msg,CC,,$@)
>   	$(CC) $(CFLAGS) -c $(filter %.c,$^) $(LDLIBS) -o $@
> +$(OUTPUT)/bench_rename.o: $(OUTPUT)/test_overhead.skel.h
>   $(OUTPUT)/bench.o: bench.h
>   $(OUTPUT)/bench: LDLIBS += -lm
>   $(OUTPUT)/bench: $(OUTPUT)/bench.o \
> -		 $(OUTPUT)/bench_count.o
> +		 $(OUTPUT)/bench_count.o \
> +		 $(OUTPUT)/bench_rename.o
>   	$(call msg,BINARY,,$@)
>   	$(CC) $(LDFLAGS) -o $@ $(filter %.a %.o,$^) $(LDLIBS)
>   
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