linux-kernel - Re: [PATCH 4/4] s390/ftrace: add -mfentry and -mnop-mcount support

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Date:   Tue, 7 Aug 2018 07:30:17 +0200
From:   Heiko Carstens <heiko.carstens@...ibm.com>
To:     Vasily Gorbik <gor@...ux.ibm.com>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 4/4] s390/ftrace: add -mfentry and -mnop-mcount support

On Mon, Aug 06, 2018 at 03:17:47PM +0200, Vasily Gorbik wrote:
> Utilize -mfentry and -mnop-mcount gcc options together with
> -mrecord-mcount to get compiler generated calls to the profiling functions
> as nops which are compatible with current -mhotpatch=0,3 approach.  At the
> same time -mrecord-mcount enables __mcount_loc section generation by
> the compiler which allows to avoid using scripts/recordmcount.pl script.
> 
> Signed-off-by: Vasily Gorbik <gor@...ux.ibm.com>
> ---
>  arch/s390/Kconfig              |  2 ++
>  arch/s390/Makefile             | 16 +++++++++-------
>  arch/s390/include/asm/ftrace.h |  6 +++---
>  arch/s390/kernel/ftrace.c      |  2 +-
>  arch/s390/kernel/mcount.S      |  2 +-
>  5 files changed, 16 insertions(+), 12 deletions(-)

Do you have numbers which tell how much this reduces the compile time of
the kernel on s390? I assume this change makes quite some difference.

Reviewed-by: Heiko Carstens <heiko.carstens@...ibm.com>