Subject: CCL:Other Processors

From: root <[email-masked]>
Date: Fri, 27 Mar 1998 17:38:24 +0300 (MSK)

Gustavo de Miranda Seabra writes:
 > Hi All,
 > 
 >     I would like to know if someone has any experience with desktop
 > processors other than Intel ones, I mean, AMD-K6 or Cyrix 6x86. What are the
 > advantages or disadvantages of these processors compared with Pentium or
 > Pentuim II processors? (At their home pages, the AMD and Cyrix processors
 > are always comparable to Intel ones.)
 
Current AMD K6 processors are somewhat weaker in concerns to their
float performance. This is worsened by the fact that code for the K6
needs to be optimized very differently than for a Pentium (K6 emulates 
Intel code by a RISC CPU kernel).

The bottom line of this is that the K6 delivers (very) roughly half the
float performance of Pentium II at the same clock frequency (of course 
the Pentium also costs significantly more). You would perhaps want to 
consider the Alpha AXP line of processors. Linux runs on the Alpha,
and  the egcs compiler makes noticeably better code than gcc. Further 
improvements are to be expected. If your code does not grab the entire 
memory bandwidth nother possibility would be a (100baseT-connected
cluster of) dual-Pentium II machines running SMP Linux (for that see
http://www.beowulf.org ).

For K6 info see:
 
http://www.tomshardware.com/k6.html
http://www.byte.com/art/9706/sec3/art1.htm

also,

http://www.amd.com should be helpful. Lots of pdf files there.

Regards, 
Eugene Leitl

---

From: Jon Wright <[email-masked]>
Date: Sat, 28 Mar 1998 09:28:28 +0800

At 16:20 27/03/98 +0100, you wrote:

>> processors other than Intel ones, I mean, AMD-K6 or Cyrix 6x86. 
>I know, there are a lot of troubles with Cyrix 6x86. A large
>ammount of programs wouldn't like to run. 
>(I didn't hear anything wrong about AMD-K6.)   

We have a selection of Cyrix 6x86L/6x86MMX
Pentium Pro
Pentium II
We've found all of them to run Win95 and Linux with no problems at all.
However for any serious FP work the Intel are 2-3x faster than the cyrix's.
>From reports AMD K6 are between cyrix and intel for FP work.
If you are going to run Fortran stuff under Linux on a x86 chip it makes
good sense to invest in a commercial compiler. We found the Portland Group
f77 generated code that ran 3x faster than g77 produced.
A few benchmarks are on my web pages:

http://www.ibms.sinica.edu.tw/~jon/machines.html
Cheers
Jon
[email-masked]

---

From: root <[email-masked]>
Date: Sat, 28 Mar 1998 13:48:44 +0300 (MSK)

Ricky A. Kendall writes:
 
 > them!  I'd also get it in writting!! :) If you want to run additional
 > OS software such as Linux then you want to stay with the pentium line.

Definitely wrong. Early versions of the K6 had _occasional_ problems
if 1) you had memory over 32 MBytes AND 2) you ran a taxing task,
e.g. a kernel build.

All current AMD K6 products are bug-free, and Linux runs great with
them. (K6 does not have the F00F bug, for instance). If you want to
make sure, look if your CPU is past C stepping, then it's definitely ok. 

Another thing entirely is float performance. If you want high absolute 
float performance, go for the Pentium Pro or Pentium II. If you are
interested in price/performance ratio, or just integer performance, go
for the AMD K6/233. (AMD K6/266 is not very cheap yet). Notice that
gcc cannot optimize for the K6 directly yet, this might change in the 
future. For the price difference, you might also want to purchase a
motherboard with 1 MByte 2nd level cache.

If you want to build a Beowulf cluster (PVM/MPI code) and your code is 
is not very memory bandwidth-hungry, you should investigate dual-CPU
boards, and Linux SMP. You even don't need a switch for 2-3 node
clusters, 2 NICs/machine and 100baseT crossover cable is
sufficient. SMP support for Linux is already adequate, and Linus
Torvalds (with Transmeta) is currently enhancing it further.

In any case there are relatively cheap 200-300 MHz Alphas (0.8-0.9 k$) 
out there, which run great with Alpha AXP. Use egcs, not gcc for your
code then. Compiler support for the Alpha is likely to grow much
better in the future. I see possible problems with Compaq's policy to
focus on NT-optimized Alpha products for their high-end servers. This
might make noncrippled CPUs hard to get in the future.

 > Cyrix chips have fewer problems with Linux than the AMD but many
 > people run Linux on all three.  There have been lots of problems
 > reported with the AMD using Linux (look at the linux news groups).  I

You should have listened closer. This is a public forum, you should
have checked twice.

 > personally would pay the difference to get the pentium based product.
 
Please think things over before you support your favourite monopoly.
Forthcoming Merced is purported to suppress free OSses since requiring 
MDA. Do you really want to face a single-source AND monopoly future?

Regards,
Eugene Leitl