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SubjectRe: [RFC PATCH v4] GCOV: profile by modules
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On 25.05.2020 12:00, gengcixi@gmail.com wrote:
> From: Cixi Geng <cixi.geng1@unisoc.com>
>
> The CONFIG_GCOV_PROFILE_ALL will compile kernel by profiling entire
> kernel which will lead to kernel run slower.Use GCOV_PROFILE_PREREQS
> to control part of the kernel modules to open gcov.

Maybe rephrase the commit message to make the intention more obvious:

Introduce new configuration option GCOV_PROFILE_PREREQS that can be used
to check whether the prerequisites for enabling gcov profiling for
specific files and directories are met.

>
> Only add SERIAL_GCOV for an example.
>
> Signed-off-by: Cixi Geng <cixi.geng1@unisoc.com>
> ---
> drivers/tty/serial/Kconfig | 7 +++++++
> drivers/tty/serial/Makefile | 1 +
> kernel/gcov/Kconfig | 14 ++++++++++++++
> 3 files changed, 22 insertions(+)
>
> diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
> index adf9e80e7dc9..6df002370f18 100644
> --- a/drivers/tty/serial/Kconfig
> +++ b/drivers/tty/serial/Kconfig
> @@ -1566,3 +1566,10 @@ endmenu
>
> config SERIAL_MCTRL_GPIO
> tristate
> +
> +config SERIAL_GCOV
> + bool "Enable profile gcov for serial directory"
> + depends on GCOV_PROFILE_PREREQS
> + help
> + The SERIAL_GCOV will add Gcov profiling flags when kernel compiles.
> + Say 'Y' here if you want the gcov data for the serial directory,
> diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile
> index d056ee6cca33..17272733db95 100644
> --- a/drivers/tty/serial/Makefile
> +++ b/drivers/tty/serial/Makefile
> @@ -3,6 +3,7 @@
> # Makefile for the kernel serial device drivers.
> #
>
> +GCOV_PROFILE := $(CONFIG_SERIAL_GCOV)
> obj-$(CONFIG_SERIAL_CORE) += serial_core.o
>
> obj-$(CONFIG_SERIAL_EARLYCON) += earlycon.o
> diff --git a/kernel/gcov/Kconfig b/kernel/gcov/Kconfig
> index 3941a9c48f83..ea8b514f5676 100644
> --- a/kernel/gcov/Kconfig
> +++ b/kernel/gcov/Kconfig
> @@ -51,6 +51,20 @@ config GCOV_PROFILE_ALL
> larger and run slower. Also be sure to exclude files from profiling
> which are not linked to the kernel image to prevent linker errors.
>
> +config GCOV_PROFILE_PREREQS
> + bool "Profile Kernel subsytem"
> + depends on !COMPILE_TEST
> + depends on GCOV_KERNEL
> + depends on !GCOV_PROFILE_ALL
> + help
> + This options activates profiling for the specified kernel modules.
> +
> + When some modules need Gcov data, enable this config, then configure
> + with gcov on the corresponding modules,The directories or files of
> + these modules will be added profiling flags after kernel compile.
> +
> + If unsure, say N.

This is not quite what I had in mind. A user still needs to manually
select GCOV_PROFILE, then GCOV_PROFILE_PREREQS, then SERIAL_GCOV.

My though was that you could provide an automatic config option that is
invisible in the configuration dialog, and that is automatically
selected when all prereqs for enabling GCOV in a module directory are met.

Something like the following:

config GCOV_PROFILE_PREREQS
bool
default y if GCOV_KERNEL && !COMPILE_TEST
default n

There's no need to add GCOV_KERNEL_ALL here since that is about a user
choice ("I want all code compiled with profiling") vs. this new symbol
which is about an ability ("all prereqs for enabling profiling in
specific directories are met).


> +
> choice
> prompt "Specify GCOV format"
> depends on GCOV_KERNEL
>


--
Peter Oberparleiter
Linux on Z Development - IBM Germany

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