Re: ICM vs. L and LTR

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1 total messages Started by NEWS Thu, 13 Aug 1992 15:30

#325

Author: NEWS
Date: Thu, 13 Aug 1992 15:30

39 lines
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In article <1992Aug12.163757.759@infonode.ingr.com> dwayne@dwayneb.b17d.ingr.com
 (Dwayne A. Blumenberg) writes:
>I've noticed lately that some recent IBM code uses
>the sequence:
>
>    L     Rx,AREA
>    LTR   Rx,Rx
>    BNZ   SOMEWHERE
>
>and I was wondering if
>
>    ICM   Rx,15,AREA
>    BNZ   SOMEWHERE
>
>would be faster?

A paper in the CME Newsletter #88 entitled "Measuring 370 Instructions"
(by Ed Stewart) talks about the author's effort to measure how fast
individual instructions are on a 3081K CPU.  Pipelining and alignment
and god knows what else all affect instruction execution rates, so
IBM doesn't quote these much anymore.

Anyway, he clocked the following instructions at the indicated MIPS:

   ICM   0,15,W1             10.4287
   L     0,W1                41.8938
   LTR   0,1                 41.7416

So it appears that -- at least on a 3081K -- the L/LTR sequence is
roughly twice as fast as the ICM.

>--
>Dwayne A. Blumenberg            | Internet:  dwayne@dwayneb.b30.ingr.com
>IBM Systems Programmer          | UUCP:      ...uunet!ingr!b30!dwayneb!dwayne
>Intergraph Corp., M.S. GD3002   | Voice:     (205) 730-3795
>Huntsville, AL  35894-0001      | FAX:       (205) 730-3300

- David Andrews
  dandrews@bilver.oau.org

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