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

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Date:   Fri, 24 Sep 2021 17:15:01 +0000
From:   Song Liu <songliubraving@...com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Andrii Nakryiko <andriin@...com>,
        "KP Singh" <kpsingh@...nel.org>
CC:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        "Masami Hiramatsu" <mhiramat@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "Jiri Olsa" <jolsa@...hat.com>, Namhyung Kim <namhyung@...nel.org>
Subject: Re: [RFC] perf/core: allow ftrace for functions in
 kernel/event/core.c



> On Jun 5, 2020, at 3:02 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> On Fri, 5 Jun 2020 21:58:48 +0000
> Song Liu <songliubraving@...com> wrote:
> 
>> 
>> How does this work in your tests? 
> 
> I started it, but got distracted by other work. It did not crash with
> the little testing I did do. I wanted to also look at my patch that
> adds tracing to the ftrace directory too.
> 
> I'll try to remember to address this some more next week. Feel free to
> ping me again then.

It looks like we dropped the ball more than a year ago. 

Adding Andrii and KP, who both hit this limitation in their recent work. 
I also hit this again recently. I was trying to use kernel live patch to 
fix a perf issue, but realized the whole kernel/events directory is not
ftrace-able. :(


Hi Steven, 

I am not sure whether you have got chance to test it more thoroughly. 
Optimistically assuming it didn't crash easily :-) , what would you 
suggest for our next steps? 

Thanks,
Song



Attaching the original RFC/PATCH below. 

From: Song Liu <songliubraving@...com>
Subject: [RFC] perf/core: allow ftrace for functions in kernel/event/core.c

It is useful to trace functions in kernel/event/core.c. Allow ftrace for
them by removing $(CC_FLAGS_FTRACE) from Makefile.

Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Steven Rostedt (VMware) <rostedt@...dmis.org>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Alexey Budankov <alexey.budankov@...ux.intel.com>
Signed-off-by: Song Liu <songliubraving@...com>
---
 kernel/events/Makefile | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/kernel/events/Makefile b/kernel/events/Makefile
index 3c022e33c109..8591c180b52b 100644
--- a/kernel/events/Makefile
+++ b/kernel/events/Makefile
@@ -1,10 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0
-ifdef CONFIG_FUNCTION_TRACER
-CFLAGS_REMOVE_core.o =3D $(CC_FLAGS_FTRACE)
-endif
-
 obj-y :=3D core.o ring_buffer.o callchain.o
=20
 obj-$(CONFIG_HAVE_HW_BREAKPOINT) +=3D hw_breakpoint.o
 obj-$(CONFIG_UPROBES) +=3D uprobes.o
-
--=20
2.24.1