Path: utzoo!mnetor!uunet!husc6!mit-eddie!uw-beaver!cornell!batcomputer!pyramid!prls!mips!mash
From: mash@mips.UUCP (John Mashey)
Newsgroups: comp.arch
Subject: Re: Why is SPARC so slow?
Message-ID: <1156@winchester.UUCP>
Date: 16 Dec 87 19:29:24 GMT
References: <1078@quacky.UUCP> <8809@sgi.SGI.COM> <6964@apple.UUCP> <344@ma.diab.UUCP> <538@esl.UUCP>
Reply-To: mash@winchester.UUCP (John Mashey)
Organization: MIPS Computer Systems, Sunnyvale, CA
Lines: 99

In article <538@esl.UUCP> ian@esl.UUCP (Ian Kaplan) writes:
...
>   I think that the discussion on the SPARC vs. the MIPS R2000 centers
>   around why the SPARC is not faster than it is - specifically, why it is
>   not as fast as the MIPS processor.  What seems to have been missed here,
>   if I properly understand Mr. Fogelstrom's article, is that the SPARC is
>   quite fast.  The lab I work in has a Sun 4/280 and I can tell you that
>   it smokes.  It may be 20% slower than the MIPS processor, but it is by
>   no means a failure.  The SPARC is much faster than the Motorola 68020 
>   and, I would bet, the National processors....

I don't think that anyone is arguing that SPARC is slower than a 68K,
or a failure. (It's not, and it isn't.)
What is going on is some serious architectural debate,
(which is what this newsgroup is for!).  Of course, some of this has
been stirred up people finally being able to get some actual data,
and then trying to understand what's going on.  Note that with one
exception [Dave Hough's careful posting a while back of various FP
benchmarks], the only performance appraisals that have been offered by Sun
to the general public [to my knowledge, I'll be glad to hear of others]:

1) The original set of benchmarks in the Sun-4 introduction publicity.
(Dhrystone, Stanford, Linpack SP, Linpack DP, and Spice).

2) Introduction materials, brochures, and advertisements:

The original announcement described the Sun-4 as ``10 mips'',
``ten times faster than a VAX 11/780'' [1], and
``in the same performance class as the VAX 8800''. [2]

"Relative to other manufacturer's high-end offerings,
the Sun-4/200 excels in floating-point performance.
In fact, the Sun-4/200 will execute floating-point-intensive applications
faster than the VAX 8800 superminicomputer." [3]

"Our new Sun-4/260, the first born of our brand new family of supercomputing
workstations and servers.  In computer-ese, it delivers the performance
of 10 MIPS.  For the sake of comparison, that's as much horsepower
as a minicomputer like the DEC VAX 8800." [4]

"SPARC is an open architecture, available today,
that Sun uses to implement the best price/performance system available, [5]
reach as low as $4000 per million instructions per second." [6]

"SPARC is the first [7] RISC architecture to incorporate the features found
in supercomputers such as Cray systems.
Single-cycle access to a large cache memory, [7a]
a large register file, [7b]
and pipelining, [7c]
features pioneered on supercomputers, are part of SPARC.
Register-to-register and load/store design, [7d] along with fixed-format [7e]
instructions and more concurrency [7f] in our architecture,
propel Sun's RISC machines to unmatched performance." [8]

"SPARC is an open, scalable architecture.
It is the most scalable [9] RISC architecture available today."

Now, of the numbered assertions, some are amenable to quantitative analysis,
by gathering data carefully and publishing it.  If properly done,
and if enough real benchmarks can be obtained, people can reach their own
conclusions about whether or not they believe these assertions.

[1], [2], [3], [4] (except horsepower is a little fuzzy: does it include
floating point? does it include multi-user performance?), [8] are
statements about performance, and should be testable.
[5] and [6] are a little more slippery, as one needs to compute performance
first, and then get costs for comparable configurations.
[7] can be analyzed by comparing with all other RISC architectures that
shipped before SPARC.
[9] is hard to evaluate, since scalability is not easily measured.

Anyway, when Forrest asks "why is SPARC slow", I think what he means
is that neither the published data nor customer benchmarking seems to
justify the conclusions reached above, and from the outside,
those are the hypotheses that the rest of us get to deal with.

Ian: since you have a 4/280, perhaps you might offer some benchmarks,
which would add to our knowledge of a (controversial) topic.
In particular, it would be wonderful if you've got any large,
actual integer applications, especially if they can be made public-domain
so that they can be run anywhere. [floating-point ones are fine, too,
but there already exist lots of those, whereas there's a sad lack of
integer ones.]
Unfortunately, saying that a machine "smokes" doesn't help as much!

Also, it would help to specify which Motorola implementation it was much
faster than: a recent Computerworld article fell into the trap of
saying the Sun-4 was exceeding expectations, because it looked 3-5X faster
(than the Sun-3), more even than the claimed 2.5X.  If you consider
2-mips 3/100s and 4-mips 3/200s, you can see what happened.

To summarize: statements about performance are either completely meaningless,
or they're actually supposed to tell something about how computers
behave.  If they're the latter, you should be able to test them.
-- 
-john mashey	DISCLAIMER: 
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