> On May 26, 2020, at 2:54 PM, Peter Zijlstra <pet...@infradead.org> wrote:
>
> On Tue, May 26, 2020 at 09:46:29PM +0000, Song Liu wrote:
>>
>>
>>> On May 26, 2020, at 2:39 PM, Peter Zijlstra <pet...@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.
>>
>> Do you have some tricky functions that we should double check?
>
> I've no idea what probe: does. iirc there's something like
> ftrace:function that is like regular function tracing.
Those are kprobes. I have CONFIG_HAVE_KPROBES_ON_FTRACE=y in .config.
>
> At some point using that made the kernel really sick due to recursion
> between ftrace and perf. Quite possibly that's been fixed, dunno.
I also tried on ctx_sched_out() and event_sched_out(). They also work
as expected.
Thanks,
Song
