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Re: Sarge, kernel-image, and i586

On Wed, Aug 25, 2004 at 12:23:54AM -0500, Adam Majer wrote:
> Matt Zimmerman wrote:
> >On Mon, Aug 09, 2004 at 02:56:15PM -0500, Adam Majer wrote:
> >
> >  
> >
> >>There is no more 586 kernel though. Not even the regular one. The 386
> >>version is quite slower on a Pentium MMX than an optimized one.
> >>    
> >>
> >
> >Have you measured this?
> >
> >  
> >
> With my stop watch. Really. KDE was at least twice as slow with a 386
> kernel than a 586mmx kernel. There is a *huge* performance penalty if
> one is running a 386 kernel. I have tried this on a Pentium 200 MMX with
> 196MB. With slow machines like this, the difference between a 386 and
> 586 can be seconds to start things like terminal or Konqueror. It is
> actually more than a minute booting up. The system is essentially
> unusable with a 386 kernel, but it is still running at a steady pace
> under a 586mmx kernel.

This is a *5*86 chip, and not a 686, right? This is not implausible;
the 586 was a *disaster* in hindsight, and an oddball in an otherwise
tidy series of chips. I believe the problem lies with the pipeline
scheduling; at any rate, you want 586-targetted code on a 586 and
486-targetted on anything else. You also want to throw your 586 in the

On the other hand, there are at least half a dozen other things that
could possibly be responsible for this, and it doesn't sound like
you've ruled any of them out. Certainly this is not compelling
evidence; you'd have to analyse exactly *why* it made a difference.

> I'm not complaining that there is no 2.6.x 586 or 586-mmx kernels since
> I can just rebuild one. But there is a huge performance loss running a
> 386 kernel on anything else than a 386 or maybe a 486 (but I haven't
> tried a 486).

This, however, is *not* true. If you have a *6*86 then the design flaw
was fixed and the problem does not occur. What's more, a 586 isn't
much happier about 686-targetted code than it is about 386-targetted
code. And nothing else likes running 586-targetted code - it can be
slower than 486-targetted code in some circumstances, when running on
a 686. The difference between 486-targetted and 686-targetted, on a
686, is small to nonexistent.

  .''`.  ** Debian GNU/Linux ** | Andrew Suffield
 : :' :  http://www.debian.org/ |
 `. `'                          |
   `-             -><-          |

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