Hi Steven, > On May 26, 2020, at 3:04 PM, Steven Rostedt <rost...@goodmis.org> wrote: > > 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.
How does this work in your tests? Thanks, Song
