Re: [RFC] perf/core: allow ftrace for functions in kernel/event/core.c

[Peter Zijlstra]

On Tue, May 26, 2020 at 09:46:29PM +0000, Song Liu wrote:
> 
> 
> > On May 26, 2020, at 2:39 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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.

At some point using that made the kernel really sick due to recursion
between ftrace and perf. Quite possibly that's been fixed, dunno.