Path: utzoo!mnetor!uunet!husc6!bloom-beacon!gatech!hubcap!ncrcae!ncr-sd!steves From: steves@ncr-sd.SanDiego.NCR.COM (Steve Schlesinger) Newsgroups: comp.arch Subject: Re: What's a Vax 11/780 MIP really? Message-ID: <2095@ncr-sd.SanDiego.NCR.COM> Date: 14 Mar 88 20:09:35 GMT References: <413@mn-at1.UUCP> <1988Mar14.002026.3977@gpu.utcs.toronto.edu> Reply-To: steves@ncr-sd.SanDiego.NCR.COM (Steve Schlesinger) Organization: NCR Corporation, Rancho Bernardo Lines: 79 >In article <413@mn-at1.UUCP> alan@mn-at1.UUCP (Alan Klietz) writes: >>A recent column in one of >>the Unix trade mags reveals that the Vax 780 = 1 MIPS rule-of-thumb >>may be grossly overstated. Omri Serlin reported that according to DEC data, A VAX 780 executes about 470 thousand instructions per second for "typical" workloads. In article <1988Mar14.002026.3977@gpu.utcs.toronto.edu> dennis@gpu.utcs.toronto.edu (Dennis Ferguson) writes: > >This is well known. I suspect you will get more than one reply (beside >this one) reiterating the story about how the DEC types benchmarked the >11/780 against a then-current 370 which IBM was calling a 1 MIPS machine, >found it to run about the same speed, and so for marketing purposes called >the 11/780 a "1 MIPS" computer. Thus the "MIPS" referred to are supposed to >be native 370 MIPS, not native Vax MIPS. I doubt if anyone really knows for sure where the axiomatic "VAX 780 = 1 mips" came from. I think it had two (possiblly related) points of origin. 1. The VAX 780 was evaluated as 1.06 mips in the August 2, 1982 Computerworld Annual Survey. I spoke to someone at Computerworld at that time. He admitted the very approximate nature of their published mips ratings. He told me that they took performance claims from vendors, did some reason checking on them and published them with suitable statements about the approximate nature of such data. As far as I know DEC wasn't publicly making claims in 1982, that the 780 was equal in performance to the canonical 1 mip IBM machine, the 370/158 Model 3. (I don't know the instruction rate of the 158-3). 2. When systems other than VAXen entered the Unix marketplace, their performance was characterized relative to a VAX. The VAX was the obvious and convenient unit. Since vendors threw around mips claims like confetti on New Year's Eve, mips was a unit that everyone understood (or so someone thought). So if new Unix box had twice the performance of a VAX 780, it was called a 2 VAX mips box while a 780 was a 1 VAX mips box. > >This, unfortunately, is also not true, at least in my experience. I have >found that you can match benchmark results on a 370 and a Vax pretty well >by multiplying the IBM-reported "MIPS" number by 1.8 or so (i.e. a 13 MIPS >3090 goes faster than one would otherwise be led to believe). I really >think some marketeer at DEC just made up the 1 MIPS number so Vaxes would >look better against the IBM 370 competition. The fact that trade magazines >are just getting around to realizing this shows what a good idea it was. Some people at Amdahl published data last year on benchmarking in the IBM and Unix worlds. They should understand this better than anyone, since they sell and evaluate systems in both performance measurement worlds. My recollection is (someone at Amdahl correct me where necessary) that if an Amdahl system was X IBM mips then the same system would be about 1.5 X times the performance of a VAX 780 (NOT VAX MIPS !!!). >All of which matters not at all, since if you simply define a 780 to be >1 "MIPS" and measure everything against it, it all works out in the end >for many practical purposes anyway. > >Dennis Ferguson >University of Toronto Yes. The Unix performance measurement world does this. Usually we state performance as relative to a VAX 780. Unfortunately, even here there is room for confusion. Different versions of Unix have different compilers and (obviously) kernels which have different performance characteristics. VAXes often perform better with VMS compilers. Which is the "real" VAX to measure against? The Unix marketing world has simplified X times the performance of a VAX 780 to X mips. Steve Schlesinger NCR Corporation Disclaimer: This is my opinion, not that of NCR Corporation.