On Tue, 26 May 2020 23:54:15 +0200 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. > > At some point using that made the kernel really sick due to recursion > between ftrace and perf. Quite possibly that's been fixed, dunno. In the early days there was a lot of issues with recursions, but I added a lot of recursion protection since then. I'll give this patch a spin and see if I can make it crash. -- Steve
