prefetching (was:Re: Future of architecture)

Have these software prefetch techniques been investigated? If so, who has
published them and/or who is doing them in a production compiler/linker?
Are they wins, and if so, by how much?




1. inst. and data prefetch with subroutine calls?


      - upstream from a procedure call, issue an inst. prefetch for
              the procedure entry point


      - upstream from a procedure call, issue a data prefetch (or line
              allocate, which omits refill) for the procedure's stack frame


      - upstream from a procedure return, issue a data prefetch for
              the caller's stack frame


      - let the linker associate global data areas with the procedures that
              use these areas, and thus upstream from a procedure call, have the
              linker insert data prefetches for the associated global data areas




2. heap management tricks?


      - in-line a routine at each malloc call site that initially allocates
              a contiguous region of multiple blocks (each of the request size)
              and then doles these out as it is re-invoked (this is similar to
              the logical record/physical record handling in I/O and might help
              increase spatial locality in large-line-size caches) -- I know of
              malloc implementations that keep separate free lists based on fixed-
              size allocations but call-site specific allocation seems like it
              could increase locality


      - some students and I tried adding a prefetch pointer to a linked list
              structure to enable us to process three list nodes per list-traversal
              iteration; we obtained a 24% improvement in per node time on an Alpha
              21164 (but we got a 162% improvement by using a circular buffer - see
              the second bullet in http://www.cs.clemson.edu/~mark/arch.html)




--
Mark Smotherman, Computer Science Dept., Clemson University, Clemson, SC
http://www.cs.clemson.edu/~mark/homepage.html
--

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