netdev - Re: [PATCH v4 2/2] selftest/bpf/benchs: Add bpf

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Date:   Wed, 1 Jun 2022 11:53:51 +0200
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Feng zhou <zhoufeng.zf@...edance.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        Xiongchun Duan <duanxiongchun@...edance.com>,
        Muchun Song <songmuchun@...edance.com>,
        Dongdong Wang <wangdongdong.6@...edance.com>,
        Cong Wang <cong.wang@...edance.com>,
        Chengming Zhou <zhouchengming@...edance.com>
Subject: Re: [PATCH v4 2/2] selftest/bpf/benchs: Add bpf_map benchmark

On Wed, Jun 1, 2022 at 10:42 AM Feng zhou <zhoufeng.zf@...edance.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?

> +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 ?

> +       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
>