alan@mn-at1.UUCP (Alan Klietz) (03/05/88)
In article <308@amelia.nas.nasa.gov> fouts@orville.nas.nasa.gov (Marty Fouts) writes: <In article <305@amelia.nas.nasa.gov> msf@amelia.nas.nasa.gov (Michael S. Fischbein) writes: <>If I remember correctly (I've got the reference here somewhere, but I'm <>sure I'll get flamed if I'm far off -- or even just a little off), tests <>on the first Ames Cray-2 showed twenty SIMULATED hot-and-heavy interactive <>edits used about 8% of one cpu. These were all running as canned scripts. <>Unfortunately, they also simulated using more than half of the available <>"outside world" i/o bandwidth. < <Actually we never ran those tests. I believe that numbers from a test <like this were derived at the University of Minnesota, although I <don't know their results. I ran those tests in 1985. The important results were, 1) Cray CPU time is not a significant overhead factor when performing simple single-keystroke operations by a reasonable number (10-20) of users. 2) The NSC Hyperchannel is not designed for transferring small packets of data. An A130 will saturate at 300 keystrokes/sec, due to the large overhead of setting up and tearing down a virtual circuit for each message. The Hyperchannel also does not perform well with asynchronous full duplex transmissions (e.g. TCP/IP). This is due to reservation deadlocks between pairs of adapters that attempt to send to each other simultaneously over what is really a half duplex trunk. Hence the development of "rvi" - remote vi that runs "ed" on the Cray-2. The general solution is to multiplex large numbers of smaller packets into larger Hyperchannel messages and send them in synchronous alternating trains. The problem is a general one, and applies to HSX, HSC, ULTRA, CNT, VMEbus, as well as Hyperchannel. See the paper, "An Investigation and Analysis of High Performance Data-links for Supercomputers", MSCTR112 (MSC Tech Report 112) for a more detailed discussion. -- Alan Klietz Minnesota Supercomputer Center (*) 1200 Washington Avenue South Minneapolis, MN 55415 UUCP: alan@mn-at1.k.mn.org Ph: +1 612 626 1836 ARPA: alan@uc.msc.umn.edu (was umn-rei-uc.arpa) (*) An affiliate of the University of Minnesota