linux-kernel - Re: [PATCH v2 01/32] tracing: Allow gcov profiling on only ftrace subsystem

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Message-ID: <20180820113213.09497e0a@gandalf.local.home>
Date:   Mon, 20 Aug 2018 11:32:13 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Shuah Khan <shuah@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 01/32] tracing: Allow gcov profiling on only ftrace
 subsystem

On Fri, 17 Aug 2018 01:29:39 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> Add GCOV_PROFILE_FTRACE to allow gcov profiling
> on only files in ftrace subsystem. This kconfig
> flag will be used for checking kselftest/ftrace

Note, I haven't heard of "kconfig flag" as the terminology. Usually, we
just say "config" or "config option".

> coverage.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> ---
>  kernel/trace/Kconfig  |   13 +++++++++++++
>  kernel/trace/Makefile |    5 +++++
>  2 files changed, 18 insertions(+)
> 
> diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> index fd6754b88f87..8decf6d8553a 100644
> --- a/kernel/trace/Kconfig
> +++ b/kernel/trace/Kconfig
> @@ -774,6 +774,19 @@ config TRACING_EVENTS_GPIO
>  	help
>  	  Enable tracing events for gpio subsystem
>  
> +config GCOV_PROFILE_FTRACE
> +	bool "Enable GCOV profiling on ftrace subsystem"
> +	depends on GCOV_KERNEL
> +	help
> +	  Enable GCOV profiling on ftrace subsystem for checking
> +	  which functions/lines are tested.
> +
> +	  If unsure, say N.
> +
> +	  Note that on a kernel compiled with this flags, ftrace will be
> +	  significantly run slower. So do not enable it for production
> +	  kernel.


I would rewrite the above as:

	Note that on a kernel compiled with this config, ftrace will
	run significantly slower.

I think we can leave out the production sentence. It should be obvious
from the "significantly slower" part.

Other than that, it looks fine to me.

-- Steve

> +
>  endif # FTRACE
>  
>  endif # TRACING_SUPPORT
> diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
> index 98d53b39a8ee..f81dadbc7c4a 100644
> --- a/kernel/trace/Makefile
> +++ b/kernel/trace/Makefile
> @@ -23,6 +23,11 @@ ifdef CONFIG_TRACING_BRANCHES
>  KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
>  endif
>  
> +# for GCOV coverage profiling
> +ifdef CONFIG_GCOV_PROFILE_FTRACE
> +GCOV_PROFILE := y
> +endif
> +
>  CFLAGS_trace_benchmark.o := -I$(src)
>  CFLAGS_trace_events_filter.o := -I$(src)
>