Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!rutgers!ucsd!chiton!cdl
From: cdl@chiton.ucsd.edu (Carl Lowenstein)
Newsgroups: comp.sys.next
Subject: Re: 68040 Math / Why so much system time?
Keywords: 68040 math, system time
Message-ID: <702@chiton.ucsd.edu>
Date: 14 Feb 91 17:54:39 GMT
References: <1991Feb14.160749.19048@batcomputer.tn.cornell.edu>
Reply-To: cdl@chiton (Carl Lowenstein)
Distribution: na
Organization: MPL of SIO at UCSD
Lines: 35

In article <1991Feb14.160749.19048@batcomputer.tn.cornell.edu> finn@batcomputer.tn.cornell.edu (Lee Samuel Finn) writes:
>Ok, I've just finished upgrading to OS2.0 and the 68040 logic board.
> I wrote a stupid program to exercise some trancendental
>arithmetic and then timed the puppy:

>4.8u 27.7s 0:38 84% 0+0k 3+0io 0pf+0w

>Nearly 86% of the execution time of this program is system, and only
>14% is user. If the call to sin() is changed to sqrt(), the statistics
>are _very_ different:

>9.0u 0.0s 0:09 99% 0+0k 1+0io 0pf+0w

>Now, all the execution time is user time.

>Why all the system time spent doing a sin()? 

1) the 68030 processor does not have built-in floating point instructions
    therefore its floating point is handled by a 68882 FPU
      which has built-in transcendental functions
        which are pretty fast.
2) the 68040 processor has a built-in floating point instructions
     which do not include transcendental functions
       which must then be handled by kernel exception traps
         which are slow and take up system time.

One hopes that eventually libm.a will be re-written to not call
the built-in transcendentals of the 68882, computing transcendental
functions using only the floating point instructions native to the
68040, and thus avoiding the exception traps.

-- 
        carl lowenstein         marine physical lab     u.c. san diego
        {decvax|ucbvax} !ucsd!mpl!cdl                 cdl@mpl.ucsd.edu
                                                  clowenstein@ucsd.edu