[rescue] ooh, pretty

[Patrick Giagnocavo +1.717.201.3366]

On Tue, Nov 19, 2002 at 01:45:49PM -0800, James Lockwood wrote:
> On Tue, 19 Nov 2002, Mike Meredith wrote:
> 
> > Don't fall into the trap of assuming Mhz=speed (Dave obviously knows
> > this) ... a quote from a supercomputing centre looking at the R8000
> > said that it was half the clock speed of the R4400 but 4 times the
> > speed (probably just looking at fp perf).
> 
> This is reasonably believable for the nicer R8k processors found in
> various Challenge configurations.  The 75MHz R8k used in the I2 is
> crippled with a small cache and less bus bandwidth.  The real reason for

If most everything fit in the smaller cache though, the code could
still run quite fast.

> A 75MHz R8k I2 should not be faster than any dual R10k Octane unless there
> is considerable disparity between other portions of the systems.  The
> Octane has greatly improved bus technology and even a relatively slow R10k
> in an Octane will outperform the R8k.

My guess: they were using code compiled specifically for the R8k.
When they ran the code on the R10k, it did run; however the
performance optimizations for the R8k led to cache misses or whatnot
on the R10k.

> CPU to memory is _the_ major bottleneck in the I2, it's nearly equalled by
> a SS5/110 and trounced by a U1/140.  The Challenges are 1.5-2x better (for

Yes, that was the part that was disappointing when I owned my I2.

Cordially
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