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Date:   Thu, 17 Jan 2019 15:02:49 +0000
From:   Song Liu <songliubraving@...com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
CC:     Peter Zijlstra <peterz@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>,
        "Alexei Starovoitov" <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>,
        David Ahern <dsahern@...il.com>,
        "Steven Rostedt" <rostedt@...dmis.org>
Subject: Re: [PATCH v10 perf, bpf-next 1/9] perf, bpf: Introduce
 PERF_RECORD_KSYMBOL



> On Jan 17, 2019, at 6:58 AM, Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
> 
> Em Thu, Jan 17, 2019 at 02:49:10PM +0000, Song Liu escreveu:
>> 
>> 
>>> On Jan 17, 2019, at 4:56 AM, Peter Zijlstra <peterz@...radead.org> wrote:
>>> 
>>> On Wed, Jan 16, 2019 at 08:29:23AM -0800, Song Liu wrote:
>>>> For better performance analysis of dynamically JITed and loaded kernel
>>>> functions, such as BPF programs, this patch introduces
>>>> PERF_RECORD_KSYMBOL, a new perf_event_type that exposes kernel symbol
>>>> register/unregister information to user space.
>>>> 
>>>> The following data structure is used for PERF_RECORD_KSYMBOL.
>>>> 
>>>>   /*
>>>>    * struct {
>>>>    *      struct perf_event_header        header;
>>>>    *      u64                             addr;
>>>>    *      u32                             len;
>>>>    *      u16                             ksym_type;
>>>>    *      u16                             flags;
>>>>    *      char                            name[];
>>>>    *      struct sample_id                sample_id;
>>>>    * };
>>>>    */
>>> 
>>> So I've cobbled together the attached patches to see how it would work
>>> out..
>>> 
>>> I didn't convert ftrace trampolines; because ftrace code has this
>>> uncanny ability to make my head hurt. But I don't think it should be
>>> hard, once one figures out the right structure to stick that
>>> kallsym_node thing in (ftrace_ops ?!).
>>> 
>>> It is compiled only, so no testing what so ever (also, no changelogs).
>>> 
>>> I didn't wire up the KSYM_TYPE thing; I'm wondering if we really need
>>> that, OTOH it really doesn't hurt having it either.
>>> 
>>> One weird thing I noticed, wth does bpf_prog_kallsyms_add() check
>>> CAP_ADMIN ?! Surely even a non-priv JIT'ed program generates symbols,
>>> why hide those?
>>> 
>>> Anyway; with the one nit about the get_names() thing sorted:
>>> 
>>> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
>>> 
>>> (thanks for sticking with this)
>>> <peterz-latch-next.patch><peterz-kallsym.patch><peterz-kallsym-bpf.patch>
>> 
>> Aha, now I get the point on perf_event_ksymbol(). Yeah this approach is 
>> definitely better. 
>> 
>> While I run more tests with these patches, could we get current in 
>> perf/core? This will enable the development of user space tools like
>> bcc. 
>> 
>> Also, I current base this set on bpf-next tree, as tip/perf/core is 
>> 4 week old. Shall I rebase the set on Linus' tree? Or shall I wait for
>> tip/perf/core?
> 
> So, can you post one last set, this time with PeterZ's Acked-by,
> assuming you're sorting out the get_names() thing, and I can try merging
> this into my perf/core branch, then pushing it out to Ingo, my perf/core
> starts from tip/perf/urgent, so should be new enough.
> 
> I'd then right after testing it send a pull request to Ingo, synching
> everything.
> 
> - Arnaldo

Thanks Arnaldo! I will send it soon. 

Song

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