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SubjectRe: [RFC] perf/core: allow ftrace for functions in kernel/event/core.c
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> On May 26, 2020, at 10:40 PM, Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> On Tue, 26 May 2020 21:46:29 +0000
> Song Liu <songliubraving@fb.com> wrote:
>
>>
>>
>>> On May 26, 2020, at 2:39 PM, Peter Zijlstra <peterz@infradead.org> wrote:
>>>
>>> On Tue, May 26, 2020 at 02:28:26PM -0700, Song Liu wrote:
>>>> It is useful to trace functions in kernel/event/core.c. Allow ftrace for
>>>> them by removing $(CC_FLAGS_FTRACE) from Makefile.
>>>
>>> Did you try using the ftrace event with perf with this on?
>>
>> I have tried a few things, like
>>
>> perf stat -e probe:perf_read -I 1000
>> perf record -e probe:__x64_sys_perf_event_open -aR
>>
>> They all work fine.
>
> Did you try using perf with function-tracer or function-graph tracer?
> If you just want to trace those functions with kprobes, you can
> build your kernel with CONFIG_KPROBE_EVENTS_ON_NOTRACE=y, which allows
> you to probe perf_read etc.

Thanks for the hint.

kprobe does work with CONFIG_KPROBE_EVENTS_ON_NOTRACE, but BPF trampoline
doesn't work. If it is safe, removing $(CC_FLAGS_FTRACE) is preferable.

Thanks,
Song

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