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Path: utzoo!watmath!watnot!watcgl!onfcanim!dave
From: dave@onfcanim.UUCP (Dave Martindale)
Newsgroups: net.unix-wizards
Subject: Re: busy looping in kernel, time question
Message-ID: <14809@onfcanim.UUCP>
Date: Thu, 17-Apr-86 12:32:11 EST
Article-I.D.: onfcanim.14809
Posted: Thu Apr 17 12:32:11 1986
Date-Received: Fri, 18-Apr-86 04:45:48 EST
References: <234@Shasta.ARPA>
Reply-To: dave@onfcanim.UUCP (Dave Martindale)
Organization: ONF, Montreal
Lines: 39

In article <234@Shasta.ARPA> alex@lancelot writes:
>
>	Assume I want to busy loop in the kernel for 100 milliseconds, how
>many times (approx) should I go around a loop which increments an int?
>
Do you *really* want to lock up the processor for that long?  sleep/wakeup
would make much better use of the processor.

But if your really want a busy loop, you realize that this depends on
what processor you are running on, which you didn't mention?  A Cray-2
and an 8088 can both run UNIX, but there is a fair difference in the number
of instructions they execute in 100 ms.

Tell you what.  Why not write a program like this:

	main(argc, argv)
	char **argv;
	{
		long i, limit, atol();

		limit = atol(argv[1]);
		for (i = 0; i < limit; i++)
			;
	}

Then run it until you find a value of the argument that gives an execution
time of 10 seconds.  Divide that number by 100, and you will know how many
times to go around a loop to get 100 milliseconds pretty accurately.


Seriously, wouldn't it have made more sense to just write the test program
and have your answer in 3 minutes, rather than posting an article that
several thousand people would read, particularly since they can't answer it
from the information given?

USENET is a wonderful resource for obtaining hard-to-find information.
I hate to see its effectiveness damaged by people using it as a crutch.

	Dave Martindale