[Sunhelp] CPUs

[James Lockwood]

On Fri, 26 Nov 1999, Gregory Leblanc wrote:

> Not to claim to be an expert...   It depends.  For some things, the SM81
> will be faster because of it's larger cache, while for others the HS150 (I
> think that's the number) will take the race.  150MHz with .5MB of cache, or
> 85MHz with 1 MB of cache.  I would expect the HS to be faster most of the
> time, and always cooler.  I just spent yesterday trying to find a fan with
> enough oomph to add to my 20 for cooling, and I only have a pair of SM41s.

The SuperSparc CPU's can do 3-way issue, compared with 2-way in the
HyperSparcs.  This means that the effective clockspeed advantage of the
HyperSparc is only 17% instead of 76%.

SPEC is not a perfect benchmark but it usually gets you in the ballpark:

System            CPU        ClkMHz  Cache      SPECint SPECfp  Info
Name              (NUMx)Type ext/in  Ext+I/D      92      92    Date
================= ========== ======= ========== ======= ======= =====
Sun SS20/71       SuprSP2    50/75   1M+20/16    125.8   121.2  Jan95
Sun SS20/81       SuprSP2    50/85   1M+20/16    148.6   141.4  Jan95
Sun SS20/151      HyperSP    50/150  512+8/0     169.4   208.2  Nov95

Note that there are several results for the SM81 floating around, this
seems to be about the average.  The SM81 actually exhibits superlinear
speedup from the SM71 as it supports multiple command queueing on the
mbus, allowing it to saturate it more effectively.

Generally, a 150+MHz HyperSparc will be the fastest.  If your code fits in
the 1MB cache of an SM81 or does a lot of context switches, the SM81 may
well be faster (as the SM81 uses physical cache vs the virtual cache of
the HyperSparc which has to be dumped whenever the physical/virtual
mappings change).

The HyperSparcs generally run hotter than the SuperSparcs.  The CPU
generates a lot more heat than the cache SRAMs, and the cache controller
is integrated into the same package as the CPU.

To the original poster I ask you this: why do you want to upgrade a SS20
to this point?  Unless you must run SunOS 4 (or NeXTstep, I suppose) a low
end Ultra will be a better deal.  Even the Ultra 1/140 has far greater
memory bandwidth than the SS20 does, and you strain that bandwidth more
with each additional processor.

The SS20 is a great machine, one of the best "desktops" that Sun ever
made.  But it's not an Ultra.

BTW, anyone got any extra SM50's?  :)

-James