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SubjectRe: [PATCH 4/4] s390/ftrace: add -mfentry and -mnop-mcount support
On Tue, Aug 07, 2018 at 07:30:17AM +0200, Heiko Carstens wrote:
> 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@linux.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.
>

Very roughly, best time across several runs. With -j24 on 24 core lpar
with -mfentry -mrecord-mcount etc
real 0m54.748s
user 12m32.041s
sys 1m17.778s

vs -mhotpatch=0,3 + scripts/recordmcount.pl:
real 0m56.752s
user 12m52.386s
sys 1m35.873s

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