Messages in this thread | | | From | Song Liu <> | Subject | Re: [RFC] perf/core: allow ftrace for functions in kernel/event/core.c | Date | Tue, 26 May 2020 22:08:37 +0000 |
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> On May 26, 2020, at 2:54 PM, Peter Zijlstra <peterz@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 <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. >> >> 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
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