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From: rtrauben@cortex.Eng.Sun.COM (Richard Trauben)
Newsgroups: comp.arch
Subject: Re: 64 bits for times....
Message-ID: <703@exodus.Eng.Sun.COM>
Date: 23 Aug 90 21:18:13 GMT
References: <5539@darkstar.ucsc.edu> <13285@yunexus.YorkU.CA> <30728@super.ORG> <26012@bellcore.bellcore.com> <11187@alice.UUCP> <1990Aug23.022416.14798@sco.COM>
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Organization: Sun Microsystems, Mt. View, Ca.
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>seanf@sco.COM writes:
>If you want to find out *exactly* how
>many clock-ticks an instruction takes, you do something like:
>
>       ld.l    r1, CLOCK
>       <instr>
>       ld.l    r2, CLOCK
>       sub.l   r3, r1, r2
>

Nope. (close but no cigar...)

You just measured the execution time sum of TWO instructions:
<instr> PLUS <ld> execution time where the <ld> includes bus 
arbitration and memory access time to the TOD clock resource.  

In most systems the latter term dominates. Unless <instr> is the
kind of instruction you want to drop anyway. -:) 

-Richard