Messages in this thread | | | Date | Wed, 1 Jun 2022 19:17:48 +0800 | Subject | Re: Re: [PATCH v4 2/2] selftest/bpf/benchs: Add bpf_map benchmark | From | Feng Zhou <> |
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在 2022/6/1 下午5:53, Alexei Starovoitov 写道: > On Wed, Jun 1, 2022 at 10:42 AM Feng zhou <zhoufeng.zf@bytedance.com> wrote: >> +struct { >> + __uint(type, BPF_MAP_TYPE_HASH); >> + __type(key, u32); >> + __type(value, u64); >> + __uint(max_entries, MAX_ENTRIES); >> +} hash_map_bench SEC(".maps"); >> + >> +u64 __attribute__((__aligned__(256))) percpu_time[256]; > aligned 256 ? > What is the point?
I didn't think too much about it here, just referenced it from tools/testing/selftests/bpf/progs/bloom_filter_bench.c
> >> +u64 nr_loops; >> + >> +static int loop_update_callback(__u32 index, u32 *key) >> +{ >> + u64 init_val = 1; >> + >> + bpf_map_update_elem(&hash_map_bench, key, &init_val, BPF_ANY); >> + return 0; >> +} >> + >> +SEC("fentry/" SYS_PREFIX "sys_getpgid") >> +int benchmark(void *ctx) >> +{ >> + u32 key = bpf_get_prandom_u32() % MAX_ENTRIES + MAX_ENTRIES; > What is the point of random ? > just key = MAX_ENTRIES would be the same, no? > or key = -1 ?
If all threads on different cpu trigger sys_getpgid and lookup the same key, it will cause "ret = htab_lock_bucket(htab, b, hash, &flags); " the lock competition here is fierce, and unnecessary overhead is introduced, and I don't want it to interfere with the test.
> >> + u32 cpu = bpf_get_smp_processor_id(); >> + u64 start_time = bpf_ktime_get_ns(); >> + >> + bpf_loop(nr_loops, loop_update_callback, &key, 0); >> + percpu_time[cpu & 255] = bpf_ktime_get_ns() - start_time; >> + return 0; >> +} >> -- >> 2.20.1 >>
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