Subject: Re: Mips chips/performance

From: Andreas Busse <[email-masked]>
Date: Wed, 11 Aug 93 09:35:20 +0200

> Here's a little performance table:
>	SpecINT Spec FP92 	Mhz	Cache
> Mips 3000 	27.3  	29.3    40      0+128k	    Dec 5240 numbers
> 486/66	32	16 	33/66	8k	    Intel announcement*
> 4000PC	35	34	50/100	8k+8k	    Sgi periodic chart
> 4200	  	55	30	40/80	8k+16k?	    Nec Broshure (no details)*
> 4000SC	60	58	50/100  8k+8k+1MB   SGI periodic chart
> Powerpc   	60+	80+	66	32k	    Motorolla ad *
> Pentium   	64.5	56.9	66	8k+8k	    Intel announcement * 
> R4400SC	97	88	75/150	16k+16k+1MB SGI periodic chart.
> 
> * = Spec numbers are probably obtained using an unmentioned 2nd level cache.
> 
> IMHO anything at the 4200 performance level or above looks great to me.
> 
> Question is how does the 4200 get it's speed?  It running 20% slower then the
> mips 4000PC, and supposedly has longer pipelines, and less fp support.
> 
> Is it possible it supports a second level cache? Or it it just above a very
> important 1st level cache threshold that gives it twice the perfomance of the
> 4200 for this benchmark? (I.e. in real world not faster then the 4000PC)
> 
> Or was the 4200 paired with some custom memory subsystem that implemented
> a seperate cache controller for the 2nd level cache? 

1. The specs for the R4200 are probably *estimates*. I'm sure they are
   a bit too high, but not much. The speed of the R4200 must be in
   between a R3000/40 and a R4000PC/50, simply because
   - it has 10 MHz clock less than the R4000PC/50 and
   - it has 64bit wide bus and logic, which makes it faster than a R3000/40.

2. The FP92 specs of the R4200 are so good because most floating point
   instructions have the same execution time as a real R4000 FPU has,
   only MUL and DIV are slower.

3. The pipeline is the same as a R3000 has. No reason to be slower
   than a R3000.

4. The R4200 has a larger primary cache (16k I + 8k D) than the R4000
   (8k I + 8k D). I mentioned already that the MIPS R4000 machine I
   am working on is sometimes 3 (!!) times slower than the R3000 machine
   with 32+32k cache we have here too.
   Although I don't believe that those 8k more speeds up the R4200
   by nearly factor 2 (in comparison to the R4000PC), I'm sure that
   the larger I cache results in a noticeable sustained speed up.

5. The R4200 ***DOES NOT*** support 2nd level cache. The Blockdiagram
   of ARCset shows no 2nd level cache, and there's ***NO SUPPORT*** at all.

The latter point should be one reason more to stop that 2nd level cache
discussion. If we are going to use the ARCset, we won't have 2nd level
cache. This is a fact unless someone finds an application around the R4200
or Orion *with* 2nd level cache support.
I'm not interested to spend any time to make an SC thing out of a PC CPU.
Of course, 2nd level cache would speed up the thing, but I thought that
we agreed to use an existing design to speed up development. That means
that we would use the ARCset design primarily *as is*, perhaps with
little changes in the I/O area. Integrating 2nd level cache in a design
which is not intended for that is probably no good idea.

Finally, I simply don't understand why this discussion came up.
I thought our goal was to design and produce a board with very good
price/performance relation. Although the price of the ARCset isn't
clear at the moment (which is not my or our fault, but NEC's) it seems
that this is what we are looking for. It offers more speed than
a R3081 solution probably for only few $s more.

If you all insist on a 2nd level cache design, we should forget
about the ARCset. That means in turn that we should forget about
having a design within the next 12 months. I'm not sure what then
happens to the group...

Andy

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From: [email-masked] (Ronald Schalk)
Date: Wed, 11 Aug 1993 11:45:43 +0200 (CET)

>    - it has 64bit wide bus and logic, which makes it faster than a R3000/40.

I guess by now we can close this discussion by voting for R4200.
Why:   1 This project started with the R3K andthe R4.2K is much faster,
         and this HAS FP-support. (No more discussion like 3051<->3081)

       2 It would make software easier, no FP-emulation needed :-)

       3 There are more important issues that have been put to the background
         e.g. ethernet,scsi,video,serial I/O, parallel ports, sound (?)

>    only MUL and DIV are slower.

Yes, especially considering that the R3051 was first seriously considered.

>    the larger I cache results in a noticeable sustained speed up.

YES, I guess that's important too.

> or Orion *with* 2nd level cache support.

Yes, it's important to drwaw the line somewhere, there's always something
bigger, better, faster, etc. But the main point is that the board has to
be affordabable. I guess the R4.2K gives us a viable alternative to the R3K.

Well closing off: 

Can we perform some kind of vote on the processor? Even though the 
pricing is not quite clear yet. I guess we can start talking again about 
the above mentioned issues??

Greetings Ronald

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---

From: [email-masked]
Date: Wed, 11 Aug 93 11:56:45 +0200

You write: 
Sie schreiben: 

> pricing is not quite clear yet.

Sure.  I put in mine for either R4kPC, or R4200.

--Toby.
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