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    SubjectRe: [RFC] perf/core: allow ftrace for functions in kernel/event/core.c
    On Tue, 26 May 2020 23:54:15 +0200
    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.
    >
    > 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

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