Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!think.com!linus!alliant!jgreen
From: jgreen@Alliant.COM (John C Green Jr)
Newsgroups: comp.arch
Subject: Re: Anything wrong with the i860
Summary: i860 "sweet spot" enlarged by multi-level cache
Message-ID: <4690@alliant.Alliant.COM>
Date: 20 May 91 18:32:01 GMT
References: <848@llnl.LLNL.GOV> <1991May16.221437.10751@rice.edu>
Organization: Alliant Computer Systems, Littleton, MA
Lines: 51

Eugene D Brooks III <llnl.gov> and Preston Briggs <rice.edu> have mentioned the
size of the i860 "sweet spot". Alliant builds the FX/2800, an air cooled
supercomputer from multiple i860s with global shared memory and has extensive
experience in looking for, finding, and expanding the "sweet spot."

RISC microprocessors, including the i860 need lots of bandwidth. Alliant
believes the way to deliver this bandwidth to the i860 is a multiple level
cache:

    Location    Size                          Bandwidth Per Processor
    =========== ============================= =======================
    On chip        4 KB Instruction+8 KB Data  960 MB/sec
    On board     256 KB                        128 MB/sec
    Global        16 MB                         80 MB/sec
    Main Memory 4096 MB                         40 MB/sec

If your program does enough data reuse to make most of its memory references
out of cache then it will run well. The i860 "sweet spot" may be small, but the
Alliant caches enlarge it to include:

    Advertised speed of light            2240 MFLOPS SP
    Advertised speed of light            1120 MFLOPS DP
    SPECthru                              313
    Linpack 100x100                        31 MFLOPS DP
    Linpack 1000x1000                     325 MFLOPS DP
    Convolution (500 filterx50,000 data) 2150 MFLOPS SP
    2-D FFT (Complex 1K)                  420 MFLOPS SP
    Matrix Multiply 1000x1000 (DGEMM)     985 MFLOPS DP (DP REAL matrix)
    Matrix Multiply 1000x1000 (ZGEMM)    1018 MFLOPS DP (DP COMPLEX matrix)

To put this in perspective:

* As of Dongarra's 3/19/91 Linpack report the 100x100 31 MFLOPS was the fastest
  air cooled system available. The next fastest was a NEC SX-1E eeking out 32
  MFLOPS for $Millions more.

* Also as of 3/19/91 the Linpack 1000x1000 325 MFLOPS was the fastest air
  cooled system available. The next fastest are the late ETA10-E at 334 MFLOPS
  and the Cray-2/4-256 at 360 MFLOPS.

* Getting more realistic in price: on May 7 Convex announced the $8 Million air
  cooled GaAs C3800. This machine's advertised speed of light is 960 MFLOPS DP
  and 1920 MFLOPS SP. In important scientific library routines the Alliant i860
  killer micro delivers 1018 and 2150 MFLOPS, i.e. greater than the C3800 speed
  of light for about 1/5 the price.

* The Alliant FX/2800 was announced in Jan 1990 and shipped in Mar 1990. The
  FX/800 verstion starts at $189K.

* As Eugene Brooks has said: "Nothing will survive the attack of the killer
  micros."