netdev - Re: [PATCH iproute2-next] Makefile: pass -pipe to the compiler

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Message-ID: <CAGnkfhy9-GrxtBw4bGtxVv3erbd8dRi_BRP=k2etQRj_RwuLfA@mail.gmail.com>
Date:   Sun, 14 Jul 2019 18:36:08 +0200
From:   Matteo Croce <mcroce@...hat.com>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     netdev <netdev@...r.kernel.org>, David Ahern <dsahern@...nel.org>
Subject: Re: [PATCH iproute2-next] Makefile: pass -pipe to the compiler

On Tue, Jun 11, 2019 at 9:28 PM Stephen Hemminger
<stephen@...workplumber.org> wrote:
>
> On Tue, 11 Jun 2019 20:05:13 +0200
> Matteo Croce <mcroce@...hat.com> wrote:
>
> > Pass the -pipe option to GCC, to use pipes instead of temp files.
> > On a slow AMD G-T40E CPU we get a non negligible 6% improvement
> > in build time.
> >
> > real    1m15,111s
> > user    1m2,521s
> > sys     0m12,465s
> >
> > real    1m10,861s
> > user    1m2,520s
> > sys     0m12,901s
> >
> > Signed-off-by: Matteo Croce <mcroce@...hat.com>
>
> Why bother, on my machine (make -j12).
>
> Before
> real    0m6.320s
> user    0m30.674s
> sys     0m3.649s
>
>
> After (with -pipe)
> real    0m6.158s
> user    0m31.197s
> sys     0m3.532s
>
>
> So it is slower. Get a faster disk :-)
>

I did it :)

root@apu:~# hdparm -t /dev/sda

/dev/sda:
 Timing buffered disk reads: 1086 MB in  3.00 seconds = 361.58 MB/sec

No change at all thought. It's really a CPU bound job, and this
machine is not a number cruncher:

root@apu:~# dd if=/dev/zero bs=1G count=1 status=none |time -p sha1sum
2a492f15396a6768bcbca016993f4b4c8b0b5307  -
real 16.00
user 12.38
sys 2.05

I think that the slight increase is due to the fact that the processes
starts in parallel, instead of being serialized.

> Maybe allow "EXTRA_CFLAGS" to be passed to Makefile for those that
> have a burning need for this.

Just out of curiosity, I checked the linux history repo to discover
when it was introduced in the kernel, it tooks me a while to really
find it:

Linux-0.99.13k (September 19, 1993)

-- 
Matteo Croce
per aspera ad upstream