Date: Wed, 21 Jan 2004 15:58:59 +1100 (EST) From: Bruce Evans <bde@zeta.org.au> To: John Baldwin <jhb@FreeBSD.org> Cc: Ruslan Ermilov <ru@FreeBSD.org> Subject: Re: Release Building and /etc/make.conf Message-ID: <20040121153615.O7322@gamplex.bde.org> In-Reply-To: <200401201319.52943.jhb@FreeBSD.org> References: <200401190738.i0J7ccF3020266@postoffice.e-easy.com.au> <20040121005140.D4640@gamplex.bde.org> <200401201319.52943.jhb@FreeBSD.org>
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On Tue, 20 Jan 2004, John Baldwin wrote:
> On Tuesday 20 January 2004 09:41 am, Bruce Evans wrote:
> > bsd.cpu.mk should rarely be edited, but /etc.make.conf is per-machine so
> > you can put anything you want in it. However, defaulting to
> > -mcpu=pentiumpro is just a bug, so I edit it out of bsd.cpu.mk. It
> > just micro-pessimizes for all CPUs that aren't pentium pros. This is
> > almost harmless for i386's because no one uses them, and almost harmless
> > for P3's and maybe P4's because they share some bottlenecks with
> > pentiumpros, but Athlons handle naive i386 code better than pentiums so
> > many of the pentiumpro optimizations are pessimizations for athlons.
>
> The choice if ppro was Peter's suggestion. Feel free to offer a better
> default CPU to tune for.
i386 (or equivalently, no special tuning) is the best default, at least
in non-FPU-intensive applications. In my integer crunching application/
benchmark (searching a game tree), it even gives better results than
-mcpu=pentiumpro on a pentiumpro class machine (a 366MHz Celeron).
-mcpu=athlon-xp gives even better results.
All with -O3 -fomit-frame-pointer
-mcpu-athlon-xp 48.42 real 47.31 user 0.41 sys
51.22 real 50.10 user 0.30 sys
-mcpu=i386 51.98 real 50.18 user 0.34 sys
-mcpu=pentiumpro 56.38 real 55.26 user 0.34 sys
-mcpu=pentium2 56.24 real 55.25 user 0.36 sys
-mcpu=pentium3 56.59 real 55.25 user 0.40 sys
-mcpu=pentium4 58.52 real 56.96 user 0.36 sys
-mcpu=i486 79.17 real 77.69 user 0.32 sys
-mcpu=i586 74.80 real 73.07 user 0.48 sys
This is just one benchmark, chosen for its potential optimizability.
I only did non-exhaustive benchmarks for the makeworld benchmark. I
removed the -mpentiumpro change when I saw the kernel size bloat that
it gave.
> > Note that CPUTYPE has worse bugs for i386's. Setting it to a supported
> > CPU gives -march instead of -mcpu, so using it gives unportable binaries,
> > and bsd.cpu.mk provides no way to get the corresponding -mcpu settings.
> > OTOH, CPUTYPE for alphas gives only -mcpu.
>
> That is by design. Note that on all non-i386 architectures such as alpha,
> etc. -mcpu means the same thing as -march. The other architectures use
> -mtune to get the same effect as -mcpu on i386.
Doesn't make it any less of a bug.
[Context with same benchmark on an athlon-xp lost.]
Bruce
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