Optimizationn questions?

Gary Kline kline at tao.thought.org
Thu Mar 15 05:39:03 UTC 2007

On Thu, Mar 15, 2007 at 02:47:42AM +0100, Karol Kwiatkowski wrote:
> Gary Kline wrote:
> > 	Two quick one for kernel and/or compiler wizards:  first, is
> > 	a 400Mz processor considered a 586 (for my KERNELCONF file)?
> That depends on processor architecture rather than clock frequency. Have
> a look at dmesg output - for example, Intel Celeron 400Mhz is a 686
> class processor (I686_CPU in the kernel configuration file):
> % dmesg
> % [...]
> % CPU: Pentium II/Pentium II Xeon/Celeron (400.91-MHz 686-class CPU)
> % [...]

	Dunno anything about the Xeon, but the Kayak is nuilt like a
	tank and has got to be == a 686 also.  I'll check my dmesg 
	too.  --Until very recently, I've gone wit the default (i386??);
	like: how much faster is gcc tweaking going to be?  I guess I'll
	find out!

> > 	Second, is it safe to do a buildworld with -O3?  If there are
> > 	stability concerns, I'll go with the default when I rebuild my
> > 	6.2 systems.
> If you're going to do stability/performance/compatibility tests go
> ahead. In any other situation just stick with the defaults, which on
> 6.2-RELEASE for my Celeron are:
> # (cd /usr/src && make -V CFLAGS )
> -O2 -fno-strict-aliasing -pipe -march=pentiumpro
> Note that '-march=pentiumpro' comes from setting 'CPUTYPE=i686' in
> /etc/make.conf (examples in /usr/share/examples/etc/make.conf).

	Martin Tournoij pointed out what (fine-print) I didn't see
	[never read/very seldom read] that the world and kernel should be
	left at O, O2 or their default.  I signal to gcc to unroll loops
	and know that the compiler writers are going to use their 
	learned and practical wisdom regarding loop unrolling... .

> HTH,

	It has and thanks much.  Gotta rebuild, but no big deal!


> Karol
> -- 
> Karol Kwiatkowski   <karol.kwiat at gmail dot com>
> OpenPGP 0x06E09309

  Gary Kline  kline at thought.org   www.thought.org  Public Service Unix

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