Man, my typing sucked in that last one...
Mike A. Harris wrote:
On Mon, 21 Oct 2002, Thomas Dodd wrote:
Except a i586 kerenl is horrribly slow on a K6.
I've never done an in depth comparison, but I wouldn't consider
it to be all that bad. The K6 should reorder things internally I
would presume anyway to be more optimal. Have you done any
Not sure there. The instruction mix from the compiler should
be different, causing problems for the schedulers.
benchmarking? I used to use home brew K6 kernels, but then
switched to stock kernels not long after starting at Red Hat. QA
testing became more important to me. ;o)
No idea what to bench with. The whole problkem with benckmarking
is timing the right things and figuring out what it means :)
So owners of a true Pentium would probably benifit from
a -mcpu=i586 version of glibc.
Since it would give a more optimum instruction mix.
My understanding is that the i586 scheduler (compiler) creates
code that only runs well on an actuall *ntel Pentium. Not a K5,
K6, or Cyrix. Not a i686 (PPRo, PII, or PIII), not a Pentium w/
MMX.
That is a reasonable assumption. Note however that newer CPU's
internally reorder instruction execution to be more optimal at
runtime.
When the PII and K6-2 came out, I remember the optimization
guide saying that the new CPUs ran i386 optimized code faster
than pentium optimized code, and to not use the pentium
guidelines anymore.
There is no question at all, that providing a kernel customized
for every single CPU brand/model would be most optimal for that
particular CPU brand/model. That isn't however remotely
Didn't mean that ;)
But if most pre i686 CPUS (pre PPro/PII/Athlon) run the i386 code
mix faster than the pentium mix, why not supply the i386 mix.
I woul thing there are more 486s, P/MMX, K5, K6, and Cyrix CPUs
still in use than Pentiums (pre MMX).
An athlon glibc would be nice to test. Not sure if it would
provide noticeable difference or not as I'm not sure if gcc
takes advantage of anything new in the athlon instruction set or
not. Athlon optimized string operations would be nice, but I
don't think gcc takes advantage of anything that useful on athlon
yet. It'd be very cool though to have if one of the compiler
guys could provide info about gcc's athlon optimizations, and if
someone would implement useful tidbits if it hasn't been done
already.
If anyone experiments with a glibc rebuild, be sure to do some
before and after benchmarking with useful tests and post back to
the list.
I'd give it a crack myself, but I don't have an Athlon handy to
muck around with. ;o/
I'd do it, but I havent a clue how to build glibc that way, or
how to test the results.
-Thomas
