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- Newsgroups: comp.sys.sgi
- Path: sparky!uunet!cs.utexas.edu!sdd.hp.com!mips!odin!fido!zola!zuni!anchor!olson
- From: olson@anchor.esd.sgi.com (Dave Olson)
- Subject: Re: R4000 compiler directive, is there one ???
- Message-ID: <olujgk4@zuni.esd.sgi.com>
- Sender: news@zuni.esd.sgi.com (Net News)
- Organization: Silicon Graphics, Inc. Mountain View, CA
- References: <oisl0q0@zuni.esd.sgi.com> <1992Aug16.210505.18316@megatek.uucp>
- Date: Mon, 17 Aug 92 04:43:12 GMT
- Lines: 56
-
- In <1992Aug16.210505.18316@megatek.uucp> rgs@megatek.uucp (Rusty Sanders) writes:
-
- | From article <oisl0q0@zuni.esd.sgi.com>, by olson@anchor.esd.sgi.com (Dave Olson):
- | > In <1992Aug14.180101.14529@megatek.uucp> rgs@megatek.uucp (Rusty Sanders) writes:
- | > | Net result; if you're using floating point on an R4000 you probably
- | > | should use -mips2 -r4000 to get best performance. Does MIPS/SGI
- | > | actually support (i.e. accept bug report calls) on the undocumented
- | > | -r4000 switch?
- | >
- | > I don't think so. If so, we would have used it in the specmark
- | > tests, more than likely. I don't know why it isn't supported;
- | > it may be for lack of testing, or introduction of bugs.
- |
- | It's my understanding that MIPS specifically did NOT want to use
- | code optimized specifically for the R4000 in the Specmark suite.
- | To wit: I believe the code wasn't even compiled -mips2 (which
- | is clearly supported), much less with -r4000.
-
- I can't speak for MIPS, but SGI definitely used -mips2 on most
- of the SPEC benchmarks, see the forthcoming SPEC newsletter, and
- the preliminary Crimson results in the last one.
-
- | I have been lead to believe this is because MIPS wanted to
- | accurately represent processor performance with code compiled
- | to run on any MIPS machine, hence the -mips1 compile switch.
-
- Again, somebody from MIPS will have to comment.
-
- | I don't believe I've ever seen Specmark numbers for an R4000
- | with the code compiled -mips2 -r4000, or even just -mips2
- | (although I would dearly love to).
-
- See above.
-
- | One would think it prudent marketing for MIPS/SGI to release
- | both sets of numbers. One for compatibility mode (useful for
- | software houses, which will compile -mips1), and one for raw
- | "fast as we can get it" mode, which is the most useful number
- | for the embedded market and end-users. Not that Spec is terribly
- | useful as a performance indicator in the embedded market, but
- | it would make my discussions with management SO much easier.
-
- You may think it prudent, but as one of the people who had to run
- them, I would politely say "no thanks!". There would be a difference,
- but I don't think it will be all that huge, except perhaps for
- some of the floating point runs that do lots of loads and stores,
- since -mips2 enables [ls]dc1 as 64 bit loads and stores.
-
- Note that -mips2 still doesn't do everything the r4k is capable
- of, just those in the r6k. -mips3 will turn all the r4k stuff in
- a future compiler release (and presumably enable 64 bit ops, pointers,
- etc.)
- --
- Let no one tell me that silence gives consent, | Dave Olson
- because whoever is silent dissents. | Silicon Graphics, Inc.
- Maria Isabel Barreno | olson@sgi.com
-