linux-kernel - Re: [PATCH 2/4] trace: avoid calling cc-option -mrecord-mcount for every Makefile

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Message-Id: <your-ad-here.call-01533643171-ext-1234@work.hours>
Date:   Tue, 7 Aug 2018 13:59:31 +0200
From:   Vasily Gorbik <gor@...ux.ibm.com>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...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
Subject: Re: [PATCH 2/4] trace: avoid calling cc-option -mrecord-mcount for
 every Makefile

On Mon, Aug 06, 2018 at 11:07:40AM -0700, Andi Kleen wrote:
> On Mon, Aug 06, 2018 at 03:17:44PM +0200, Vasily Gorbik wrote:
> > Currently if CONFIG_FTRACE_MCOUNT_RECORD is enabled -mrecord-mcount
> > compiler flag support is tested for every Makefile.
> 
> Good catch.  Does it make a measurable compile time difference?
> 

A bit more than couple of seconds, but it does make a difference for a
delta build:
with patch:
real    0m9.405s
user    0m6.966s
sys     0m2.287s

without:
real    0m12.153s
user    0m9.058s
sys     0m3.026s

with -j48 on s390 24 cores lpar:
with patch:
real    0m1.949s
user    0m7.034s
sys     0m2.400s

without:
real    0m2.255s
user    0m9.243s
sys     0m3.266s

> > 
> > Top 4 cc-option usages:
> >     511 -mrecord-mcount