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Date: Mon, 6 Dec 2021 19:01:28 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Hou Tao <houtao1@...wei.com>
Cc: Alexei Starovoitov <ast@...nel.org>,
Martin KaFai Lau <kafai@...com>, Yonghong Song <yhs@...com>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next 4/5] selftests/bpf: add benchmark for
bpf_strncmp() helper
On Tue, Nov 30, 2021 at 6:07 AM Hou Tao <houtao1@...wei.com> wrote:
>
> Add benchmark to compare the performance between home-made strncmp()
> in bpf program and bpf_strncmp() helper. In summary, the performance
> win of bpf_strncmp() under x86-64 is greater than 18% when the compared
> string length is greater than 64, and is 179% when the length is 4095.
> Under arm64 the performance win is even bigger: 33% when the length
> is greater than 64 and 600% when the length is 4095.
>
> The following is the details:
>
> no-helper-X: use home-made strncmp() to compare X-sized string
> helper-Y: use bpf_strncmp() to compare Y-sized string
>
> Under x86-64:
>
> no-helper-1 3.504 ± 0.000M/s (drops 0.000 ± 0.000M/s)
> helper-1 3.347 ± 0.001M/s (drops 0.000 ± 0.000M/s)
>
> no-helper-8 3.357 ± 0.001M/s (drops 0.000 ± 0.000M/s)
> helper-8 3.307 ± 0.001M/s (drops 0.000 ± 0.000M/s)
>
> no-helper-32 3.064 ± 0.000M/s (drops 0.000 ± 0.000M/s)
> helper-32 3.253 ± 0.001M/s (drops 0.000 ± 0.000M/s)
>
> no-helper-64 2.563 ± 0.001M/s (drops 0.000 ± 0.000M/s)
> helper-64 3.040 ± 0.001M/s (drops 0.000 ± 0.000M/s)
>
> no-helper-128 1.975 ± 0.000M/s (drops 0.000 ± 0.000M/s)
> helper-128 2.641 ± 0.000M/s (drops 0.000 ± 0.000M/s)
>
> no-helper-512 0.759 ± 0.000M/s (drops 0.000 ± 0.000M/s)
> helper-512 1.574 ± 0.000M/s (drops 0.000 ± 0.000M/s)
>
> no-helper-2048 0.329 ± 0.000M/s (drops 0.000 ± 0.000M/s)
> helper-2048 0.602 ± 0.000M/s (drops 0.000 ± 0.000M/s)
>
> no-helper-4095 0.117 ± 0.000M/s (drops 0.000 ± 0.000M/s)
> helper-4095 0.327 ± 0.000M/s (drops 0.000 ± 0.000M/s)
>
> Under arm64:
>
> no-helper-1 2.806 ± 0.004M/s (drops 0.000 ± 0.000M/s)
> helper-1 2.819 ± 0.002M/s (drops 0.000 ± 0.000M/s)
>
> no-helper-8 2.797 ± 0.109M/s (drops 0.000 ± 0.000M/s)
> helper-8 2.786 ± 0.025M/s (drops 0.000 ± 0.000M/s)
>
> no-helper-32 2.399 ± 0.011M/s (drops 0.000 ± 0.000M/s)
> helper-32 2.703 ± 0.002M/s (drops 0.000 ± 0.000M/s)
>
> no-helper-64 2.020 ± 0.015M/s (drops 0.000 ± 0.000M/s)
> helper-64 2.702 ± 0.073M/s (drops 0.000 ± 0.000M/s)
>
> no-helper-128 1.604 ± 0.001M/s (drops 0.000 ± 0.000M/s)
> helper-128 2.516 ± 0.002M/s (drops 0.000 ± 0.000M/s)
>
> no-helper-512 0.699 ± 0.000M/s (drops 0.000 ± 0.000M/s)
> helper-512 2.106 ± 0.003M/s (drops 0.000 ± 0.000M/s)
>
> no-helper-2048 0.215 ± 0.000M/s (drops 0.000 ± 0.000M/s)
> helper-2048 1.223 ± 0.003M/s (drops 0.000 ± 0.000M/s)
>
> no-helper-4095 0.112 ± 0.000M/s (drops 0.000 ± 0.000M/s)
> helper-4095 0.796 ± 0.000M/s (drops 0.000 ± 0.000M/s)
>
> Signed-off-by: Hou Tao <houtao1@...wei.com>
> ---
> tools/testing/selftests/bpf/Makefile | 4 +-
> tools/testing/selftests/bpf/bench.c | 6 +
> .../selftests/bpf/benchs/bench_strncmp.c | 150 ++++++++++++++++++
> .../selftests/bpf/benchs/run_bench_strncmp.sh | 12 ++
> .../selftests/bpf/progs/strncmp_bench.c | 50 ++++++
> 5 files changed, 221 insertions(+), 1 deletion(-)
> 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/progs/strncmp_bench.c
>
[...]
> diff --git a/tools/testing/selftests/bpf/progs/strncmp_bench.c b/tools/testing/selftests/bpf/progs/strncmp_bench.c
> new file mode 100644
> index 000000000000..18373a7df76e
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/strncmp_bench.c
> @@ -0,0 +1,50 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (C) 2021. Huawei Technologies Co., Ltd */
> +#include <linux/types.h>
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +#define STRNCMP_STR_SZ 4096
> +
> +/* Will be updated by benchmark before program loading */
> +const volatile unsigned int cmp_str_len = 1;
> +const char target[STRNCMP_STR_SZ];
> +
> +long hits = 0;
> +char str[STRNCMP_STR_SZ];
> +
> +char _license[] SEC("license") = "GPL";
> +
> +static __always_inline int local_strncmp(const char *s1, unsigned int sz,
> + const char *s2)
> +{
> + int ret = 0;
> + unsigned int i;
> +
> + for (i = 0; i < sz; i++) {
> + /* E.g. 0xff > 0x31 */
> + ret = (unsigned char)s1[i] - (unsigned char)s2[i];
I'm actually not sure if it will perform subtraction in unsigned form
(and thus you'll never have a negative result) and then cast to int,
or not. Why not cast to int instead of unsigned char to be sure?
> + if (ret || !s1[i])
> + break;
> + }
> +
> + return ret;
> +}
> +
> +SEC("tp/syscalls/sys_enter_getpgid")
> +int strncmp_no_helper(void *ctx)
> +{
> + if (local_strncmp(str, cmp_str_len + 1, target) < 0)
> + __sync_add_and_fetch(&hits, 1);
> + return 0;
> +}
> +
> +SEC("tp/syscalls/sys_enter_getpgid")
> +int strncmp_helper(void *ctx)
> +{
> + if (bpf_strncmp(str, cmp_str_len + 1, target) < 0)
> + __sync_add_and_fetch(&hits, 1);
> + return 0;
> +}
> +
> --
> 2.29.2
>
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