Re: [PATCH bpf-next 4/5] selftests/bpf: add benchmark for bpf_strncmp() helper
flat view
From: Andrii Nakryiko <hidden>
Date: 2021-12-07 03:01:43
Also in:
bpf
On Tue, Nov 30, 2021 at 6:07 AM Hou Tao [off-list ref] 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 <redacted> --- 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
[...]
quoted hunk ↗ jump to hunk
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