linux-kernel - Re: [PATCH 00/34] perf clang: Builtin clang and perfhook support

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Date:   Mon, 14 Nov 2016 21:21:25 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     "Wangnan (F)" <wangnan0@...wei.com>
Cc:     Arnaldo Carvalho de Melo <acme@...hat.com>,
        Alexei Starovoitov <ast@...com>, Zefan Li <lizefan@...wei.com>,
        He Kuang <hekuang@...wei.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        pi3orama <pi3orama@....com>, Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH 00/34] perf clang: Builtin clang and perfhook support

On Mon, Nov 14, 2016 at 9:03 PM, Wangnan (F) <wangnan0@...wei.com> wrote:
>
>
> On 2016/11/15 12:57, Alexei Starovoitov wrote:
>>
>> On Mon, Nov 14, 2016 at 8:05 PM, Wang Nan <wangnan0@...wei.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?
>
>
> I can make it shorter by give it a better name or use a wrapper like
>
> BPF_MAP(update_elem)

the macro isn't pretty, since function calls won't look like calls.

> but the only thing I can't do is to make perfhook and in-kernel script
> use a uniform name for these bpf_map functions, because
> bpf_map_update_elem is already defined:
>
> "static long (*bpf_map_update_elem)(void *, void *, void *, unsigned long) =
> (void *)2;\n"

right. i guess you could have #ifdef it, so it's different for bpf backend
and for native.
Another alternative is to call it map_update_elem or map_update
or bpf_map_update. Something shorter is already a win.
'jit_helper__' prefix is an implementation detail. The users don't
need to know and don't need to spell it out everywhere.