Re: Release Building and /etc/make.conf

On Wed, 21 Jan 2004, John Baldwin wrote:

> On Tuesday 20 January 2004 11:58 pm, Bruce Evans wrote:
> > 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.
>
> Does -mcpu=althon-xp perform worse than the default in other benchmarks that
> you've run?

I haven't run enough to be sure.  It's hard to test all the combinations for
long enough.  Some quick tests with the cc1 application/benchmark:

cc1 compiled with -O3 -fomit-frame-pointer, and:
    -mcpu=i386 (code o3)
    -mcpu=i486 (o4)
    -mcpu=pentiumpro (op)
    -mcpu=athlon-xp (oa)
Times for the "all" part of "make obj; make depend; make all" starting
with an empty object tree and source tree = src/bin on the Celeron and
src/usr.sbin on the Athlon (it doesn't complete because it wants to
link to never-installed unbuilt libraries, but it gets a fair way).
Smallest real time for 2 runs:

On a Celeron 400 with source tree src/bin:
o3:      121.94 real        97.14 user        19.94 sys
o4:      130.83 real       106.59 user        19.07 sys
oa:      122.69 real        97.58 user        19.39 sys
op:      124.01 real        99.54 user        19.56 sys
All non-null -mcpu settings are pessimizations, with -mcpu=i486
significantly bad and -mcpu=pentiumpro probably significantly bad.
Optimizing the pentiumpro class machine as an athlon-xp works
better (less worse here) than optimizing it as a pentiumpro in this
benchmark too, but the differences are smaller

On an Athlon-XP1600 overclocked with source tree src/usr.sbin:
o3:       67.62 real        57.46 user         9.53 sys
o4:       69.09 real        57.65 user        10.20 sys
oa:       67.53 real        56.78 user         9.62 sys
op:       68.14 real        57.47 user         9.70 sys
Most of the differences are too small to be significant.  Optimizing
the athlon-xp as an athlon-xp at least doesn't pessimize it.

My integer-crunching benchmark shows similarly small differences on
freefall, but that may be just because freefall's gcc is so old.

> > > > 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.
>
> The intent of CPUTYPE is that you can have ports and world optimized for the
> specific machine you are compiling on, it is not set to anything by default,
> so the user only gets -march=foo if they explicitly ask for it.  I fail to
> see how that is a bug.

It is a bug because it implements the least useful option set first.

Bruce