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

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Message-Id: <20200527144040.3f12026f31b20b2011fbbcee@kernel.org>
Date:   Wed, 27 May 2020 14:40:40 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Song Liu <songliubraving@...com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        Ingo Molnar <mingo@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        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>,
        Alexey Budankov <alexey.budankov@...ux.intel.com>
Subject: Re: [RFC] perf/core: allow ftrace for functions in
 kernel/event/core.c

On Tue, 26 May 2020 21:46:29 +0000
Song Liu <songliubraving@...com> wrote:

> 
> 
> > On May 26, 2020, at 2:39 PM, Peter Zijlstra <peterz@...radead.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. 

Did you try using perf with function-tracer or function-graph tracer?
If you just want to trace those functions with kprobes, you can 
build your kernel with CONFIG_KPROBE_EVENTS_ON_NOTRACE=y, which allows
you to probe perf_read etc.

Thank you,


-- 
Masami Hiramatsu <mhiramat@...nel.org>