Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!rochester!pt!b.gp.cs.cmu.edu!ralf From: ralf@b.gp.cs.cmu.edu (Ralf Brown) Newsgroups: comp.sys.intel,comp.sys.ibm.pc,comp.unix.xenix Subject: Re: 32-bit memory benchmark results for Inboard 386/AT card Message-ID: <52@b.gp.cs.cmu.edu> Date: Sun, 28-Jun-87 20:34:31 EDT Article-I.D.: b.52 Posted: Sun Jun 28 20:34:31 1987 Date-Received: Sun, 5-Jul-87 20:15:02 EDT References: <122@spdcc.COM> <1176@bobkat.UUCP> Organization: Carnegie-Mellon University, CS/RI Lines: 34 Summary: Saving registers is time-consuming Xref: mnetor comp.sys.intel:293 comp.sys.ibm.pc:5334 comp.unix.xenix:441 In article <1176@bobkat.UUCP> m5@bobkat.UUCP (Mike McNally (Man from Mars)) writes: >In article <122@spdcc.COM> dyer@spdcc.COM (Steve Dyer) writes: > > IBM PC/AT 8mhz IBM PC/AT with Intel Inboard 386/AT > > 16-bit mem 32-bit mem > >Drystone 1.0 no reg reg no reg reg no reg reg > > 1278 1292 2293 2304 3429 3405 > >Drystone 1.1 1084 1094 1957 1963 2906 2893 > >Why is the with-register-variables time for the 32-bit version *slower* >than the without-register-variables time? Isn't that sort-of strange? >-- >Mike McNally, mercifully employed at Digital Lynx --- No, its not strange when you consider that Dhrystone is not register- intensive. Saving the registers used for register variables on entry to a procedure and restoring them at exit takes time (PUSH/POP). If the register variable is not referenced often enough that the reduced access time to the variable makes up for the overhead of pushing and popping the register. The time savings for access to a register variable may be as little as three or four clock cycles (depending on wait states), while pushing and popping take 8 to 10 clocks (again, dep on wait states). Thus, if the register variable is accessed less than four times, you have a net increase in execution time. BTW, Turbo C with all optimizations on shows the same effect on an AT when running Dhrystone. -- =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= ARPA: RALF@B.GP.CS.CMU.EDU USnail: Ralf Brown AT&T: (412) 268-3053 (school) Computer Science Department Carnegie-Mellon University DISCLAIMER? Who ever said I claimed anything? Pittsburgh, PA 15213 "I do not fear computers. I fear the lack of them..." -- Isaac Asimov