Re: [PATCH v10 perf, bpf-next 1/9] perf, bpf: Introduce PERF_RECORD_KSYMBOL

On Jan 17, 2019, at 4:56 AM, Peter Zijlstra [off-list ref] wrote:

On Wed, Jan 16, 2019 at 08:29:23AM -0800, Song Liu wrote:

quoted

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@infradead.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?

Thanks again!
Song