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From: mccalpin@masig3.ocean.fsu.edu (John D. McCalpin)
Newsgroups: comp.arch
Subject: Re: Cycle Counter
Message-ID: 
Date: 9 Aug 89 19:35:45 GMT
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Distribution: comp
Organization: Supercomputer Computations Research Institute
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In-reply-to: grunwald@flute.cs.uiuc.edu's message of 9 Aug 89 21:29:48 GMT

In the above-referenced message, Dirk Grunwald asks about cycle counters:

>I know something like this exists on the Cray X-MP; do other machines
>have cycle counters as well?

Not that it makes much difference, but the ETA-10 has several extra
registers to keep track of cycle counts for the vector and scalar units
separately.

On the FSU machine, these registers are publicly accessible, and we
have a utility which gives the fraction of vector cycles for each 
process in the system.

This makes for entertaining user's group meetings:

	Person A:"Why don't you get your !@#$^& scalar code off 
		  of our vector computer!"
	Person B:"Well, your graduate student ran a 10-hour job
		  yesterday at 0.007% vector utilization!"
	etc....

>Being able to set it would mean that you might not care if it was only
>32bits, since you set it to 0 to time routines.  With a 20 nanosecond
>clock, it would only be good for 86 seconds, but that might be enough.

The ETA-10 has 48 bits of usable integer (though it uses 64 bits of
storage).  At 142 MHz, this allows about 11.4 days before rollover,
and the machine tends to be rebooted more frequently than this....
--
John D. McCalpin - mccalpin@masig1.ocean.fsu.edu - mccalpin@nu.cs.fsu.edu
		   mccalpin@delocn.udel.edu