🚀 go-pugleaf

In article <6374@amelia.nas.nasa.gov> (Michael Yamasaki) writes:

   In article <359@garth.UUCP> fouts@bozeman.ingr.com (Martin Fouts) writes:
   >
   >One of the ways in which cheap workstations got to be cheap was by
   >neglecting to install I/O hardware.  [...]
   >
   >The single most frustrating thing for me as a consumer of workstations
   >is that I/O costs haven't decreased at the same relative rate as MIPS
   >and MFLOPS costs --- Although they are decreasing.  [...]

   >However, the cost of I/O performance is coming down.  ESDI drives with
   >hundreds of megabytes of storage are available on PCS which give the
   >same per user performance as the high performance I/O subsystems on
   >supercomputers at a lower per user cost, and usually much more storage
   >per user.
   >

   Greetings.  IMHO, one of the places where supercomputers (my only experience
   is with Cray 2 and Cray YMP) excel over the touted killer micro solution
   is in I/O performance.  In a strange way, it is because of the high cost of
   the traditional supercomputer that high cost/high performance I/O subsystems
   are acceptable.  Your last statements are (in my experience) dubious.

   My workstation (a Personal Iris) gets something less than a megabyte/second
   disk I/O.  Our Cray 2 gets something more than 10 megabytes/second.  You
   know by the magic of large I/O buffers that it can seem to the user to get
   30-40 megabytes/second.  (Wasn't HSP-2's acceptance test something like an
   aggregate 100 MBytes/second?)

   Even with IPI-2 drives, workstations and PCs will quickly run out of I/O bus
   bandwidth.  Add a HPPI or two, support for those million shaded polygons
   a second, a few hundred megabytes of memory, multiple micro processors and
   uh oh the main bus gets stressed a bit.

   There's more to supercomputer architecture than the CPU.  When micros have
   sucessfully addressed the rest of the issues, then they'll really be 
   "killers".

Hi. I completely agree that the big systems are still much better at
I/O.  The requirement for HSP-2 by the way was for real aggragate disk
performance across 10 pairs of drives at once, while maintaining an
outrageous amount of network traffic.  The Cray 2 passed with ease.
(You can't actually generate enough I/O traffic across all of the disk
drives, memory interfaces and high speed channels to consume the
"backplane" rate that the machine can generate.) The much more recent
Y/MP had to sweat a lot to pass, although it did eventually.

Now let me try to justify my last point by pointing out that I said
"per user".  A typical PC has one user.  A typical Cray 2 has
thousands, often with dozens of users on running simultaneously.  The
raw performance of the workstation is often in the 1 to 10 percent
range of the Cray, but the divisor is often 1 user for the workstation
(how many people are you sharing the iris with?) and often 10 for
simultaneous bandwidth and 1000 for storage for the Cray.

By the way, through the magic of multiple busses, some Irises (I don't
remember the personal well enough) can pass incredible amounts of data
between the graphics engine and the display without ever touching the
I/O bus.

To reitterate, you are correct; the big win in supercomputer
architecture is the scalability of I/O performance to match CPU
performance.  The big loose in "killer" microprocessor systems is the
lack of that scalability.  My argument is that we can build scalable
workstations, if we are willing to concentrate on the i/o as well as
the CPU.

One of the things which frustrates me in this area is the lack of
educational effort.  The latest book on computer "architecture" from
two people who should know better spends most of its time on CPU
performance and devotes only a small portion to I/O architecture.  Of
course, it is much better than typical "architecture" texts which only
deal with CPU architecture.


					  -Yamo-
				    yamo@wk46.nas.nasa.gov
				   yamo@amelia.nas.nasa.gov
			{ncar, decwrl, hplabs, uunet}!ames!amelia!yamo

   (hey, Marty, you gonna show up for some softball one of these days?  -Y-)

   (When's the next game.  Scuba class is over, but nobody has sent me
    a schedule in thee weeks.)

--
Martin Fouts

 UUCP:  ...!pyramid!garth!fouts  ARPA:  apd!fouts@ingr.com
PHONE:  (415) 852-2310            FAX:  (415) 856-9224
 MAIL:  2400 Geng Road, Palo Alto, CA, 94303

If you can find an opinion in my posting, please let me know.
I don't have opinions, only misconceptions.