[rescue] R8k I2's

[Joshua D Boyd]

On Tue, Jan 07, 2003 at 08:33:56PM -0500, Carl R. Friend wrote:
>    Ryan remarks:
> 
> > R8ks are hard to find.  Basically you can search for an R10k (recommended), 
> > since that one has a big boost in performance.  Otherwise, you can get an 
> > R4400 (i've got a 200mhz, runs great), and possibly replace the motherboard 
> > later on with an R10k 64-bit version (you need to replace the board to jump 
> > from R4x to R10x, because of the change in the CPU architecture).
> 
>    From all the noise I've been hearing here, I'm beginning to suspect
> that my R8k-based I2 isn't worth the floor-space it's occupying.  Whilst
> I know that's not _really_ the case, I'd like to hear some technical
> specifics as to why folks don't seem to like them.  The one I have seems
> peppy enough (but then again, I'm used to performances of an order of
> magnitude lower than most folks here....).

OK, the R8k was a stop gap measure until the R10k was ready.   SGI
needed a machine with really good floating point performance.  So, they
introduced the R8k, which used some really cutting edge design ideas to
get this performance.  One of the problems is that they traded integer
performance for floating point.  So many applications that aren't
floating point heavy ran slower on this than on previous chips.  Also,
the R8k had a deep pipeline and having to flush it was very expensive.

So, this chip relied heavily on well optimized programs, which meant
that at a minimum everything needed to be recompiled for it, and C
programs generally needed further hand optimization to prevent cache
misses. 

Anyway, when the R8k was happy, it kept up with the later released R10ks
fairly well.  However, it wasn't happy with software that wasn't made
specifically for it, which describes everything off the shelf and 
everything compiled with GCC, and so on.  I believe that writing your
software in SGI's fortran was an easy way to keep the R8k happy.
Making software more batch oriented was likely another good way.

Now, in my opinion, an R8k is in no way shape or form a waste of space.
It might not make for the best interactive desktop workstation, but for
running floating point heavy custom software, my understanding is that
it is still very usefull.  Especially when in the form of a Challenge,
like the one that George has.

-- 
Joshua D. Boyd