yoram@garfield.cs.columbia.edu (Yoram Eisenstadter) (02/13/89)
Can anybody tell me what kind of local memory has been implemented on the N.Y.U. Ultracomputer? My latest reference, which is a bit dated, states that the designers intended to place a large cache on each processing element. Is this what they've actually done, or have they taken a different approach (e.g., explicitly addressed local memory, no local memory, etc.). Thanks..Y -- Yoram Eisenstadter | Internet: yoram@cs.columbia.edu Columbia U., Dept. of Computer Science | UUCP: rutgers!columbia!cs!yoram 500 West 120th Street, Room 450 | Bitnet: yoram@cucsvm New York, NY 10027 | Phone: (212) 854-8180
edler@cmcl2.NYU.EDU (Jan Edler) (02/20/89)
Yoram Eisenstadter (yoram@garfield.cs.columbia.edu) asks about local memory in the NYU Ultracomputer. The architecture has always included a cache for each processor. In addition, we have generally considered separately addressable local memory to be a useful (but not crucial) extension to the architecture. Indeed, the prototypes we've built to date include both cache and local memory, but the local memory is fairly small (16KB) and used only for diagnostics and a few rather specific operating system purposes. If we had larger local memories, we'd begin to make it available to users, possibly restricting its use to processes that are non-preemptable, for simplicity. We could move pages around on demand as processes migrate, but our current feeling is that the benefits of jumping through those hoops are uncertain. User-accessable local memory would naturally be used for private variables. In addition, compilers could use it for temporary local copies of shared variables. Of course, these are also the purposes served by the processor cache. But there are cases, particularly in large numerical computations, where software-managed local buffering can be more effective than data cacheing given the current state of the art in cache design (LRU). Hope that helps, Jan Edler NYU Ultracomputer Research Laboratory New York University 715 Broadway, 10th floor New York, NY 10003 (212) 998-3353 edler@nyu.edu