Subject: Re: UPDATE: -pipe didn't boost up compile speed :-(
From: David Laight <email@example.com>
Date: 07/06/2002 09:44:50
On Sat, Jul 06, 2002 at 12:12:11PM +0900, Bang Jun-Young wrote:
> Arrgh. There was a stupid mistake. I forgot to add -O2 to COPTS in
> /etc/mk.conf. Sorry for the wrong results.
Yes - I built a kernel without O2, built quickly but had 7Mb of
code instead of 5Mb...
> I did the same tests again, this time with proper COPTS. To eliminate
> cache effects, I rebooted the machines between the tests.
> Athlon XP 1700 Pentium 166 Pentium 166 Pentium 166
> w/256MB w/64MB w/32MB w/16MB
> -O2 (default) 6:15 1:12:18 1:13:13 6:34:40
> -pipe -O2 6:04 1:12:55 1:13:32 manually
> aborted at
> Improvement 3% -1% -0% -100%???
> Now, it is clear that -pipe doesn't boost up kernel compile on a
> slow machine. You can benefit from it with a fast machine with enough
But it doesn't go completely 'tits up' until you get down to 16Mb.
On my (now sluggish and old) athlon 700 with 256Mb,
'rm *.o;time make' reported:
real user sys
1st build 792 556 41
2nd build 702 555 39
-pipe 1st 712 625 48
-pipe 2nd 677 687 54
(all running on a console window, fresh from reboot)
I'm not actually sure I how much I trust these figures! Note that in
the last case the 'user' time exceeds the 'real' time!
(I've might look at what these three values mean!)
> A better method to speed up build is to simply not use any optimization
> options like -O2.
That would give you a kernel that was SO big the system would never
build another one in a finite time!
David Laight: firstname.lastname@example.org