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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date: Mon, 14 Nov 2016 20:57:53 -0800
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Subject: Re: [PATCH 00/34] perf clang: Builtin clang and perfhook support
To: Wang Nan <wangnan0@huawei.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>,
        Alexei Starovoitov <ast@fb.com>, Zefan Li <lizefan@huawei.com>,
        He Kuang <hekuang@huawei.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        pi3orama <pi3orama@163.com>, Jiri Olsa <jolsa@kernel.org>
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On Mon, Nov 14, 2016 at 8:05 PM, Wang Nan <wangnan0@huawei.com> wrote:
> This is version 2 of perf builtin clang patch series. Compare to v1,
> add an exciting feature: jit compiling perf hook functions. This
> features allows script writer report result through BPF map in a
> customized way.

looks great.

>   SEC("perfhook:record_start")
>   void record_start(void *ctx)
>   {
>         int perf_pid = getpid(), key = G_perf_pid;
>         printf("Start count, perfpid=%d\n", perf_pid);
>         jit_helper__map_update_elem(ctx, &GVALS, &key, &perf_pid, 0);

the name, I think, is too verbose.
Why not to keep them as bpf_map_update_elem
even for user space programs?

>   SEC("perfhook:record_end")
>   void record_end(void *ctx)
>   {
>         u64 key = -1, value;
>         while (!jit_helper__map_get_next_key(ctx, &syscall_counter, &key, &key)) {
>                 jit_helper__map_lookup_elem(ctx, &syscall_counter, &key, &value);
>                 printf("syscall %ld\tcount: %ld\n", (long)key, (long)value);

this loop will be less verbose as well.