linux-kernel - Re: [RFC PATCH v4] GCOV: profile by modules

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Date:   Mon, 1 Jun 2020 18:56:04 +0800
From:   Cixi Geng <gengcixi@...il.com>
To:     Peter Oberparleiter <oberpar@...ux.ibm.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>, jslaby@...e.com,
        linux-serial@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Orson Zhai <orsonzhai@...il.com>, zhang.lyra@...il.com,
        Cixi Geng <cixi.geng1@...soc.com>
Subject: Re: [RFC PATCH v4] GCOV: profile by modules

Peter Oberparleiter <oberpar@...ux.ibm.com> 于2020年5月28日周四 下午10:47写道：
>
> On 25.05.2020 12:00, gengcixi@...il.com wrote:
> > From: Cixi Geng <cixi.geng1@...soc.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@...soc.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).
>
As far as I'm concerned, The GCOV_KERNEL_ALL will conflict with
GCOV_PROFILE_PREREQS，since the GCOV_KERNEL_ALL will profing all
code which contain the new config.
>
> > +
> >  choice
> >       prompt "Specify GCOV format"
> >       depends on GCOV_KERNEL
> >
>
>
> --
> Peter Oberparleiter
> Linux on Z Development - IBM Germany