2009-05-15 20:01:56 +00:00
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<META name="author" lang="en" content="Michiel Broek">
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<META name="copyright" lang="en" content="Copyright Michiel Broek">
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<META name="description" lang="en" content="MBSE BBS Manual">
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<TITLE>System load and the usleep() call.</TITLE>
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<BLOCKQUOTE>
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2011-05-22 19:21:15 +00:00
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<!-- MBSEADVERT -->
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2009-05-15 20:01:56 +00:00
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<div align='right'><h5>Last update 23-Jan-2004</h5></div>
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<div align='center'><H1>System load and the usleep() call.</H1></div>
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At some time when developping MBSE BBS I decided that background utilities
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did't need full speed to do their jobs. BBS utilities under DOS needed
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to run as fast as possible because you needed to bring the bbs down to run
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these programs and users couldn't login during that time.
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<p>
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Starting with mball, the allfiles creator, I inserted code that does usleep(1)
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after each 5 processed files. The 1 microsecond is not really the time the
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program pauses, it's probably a lot longer. I think this depends on the
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hardware type, (Intel, Sparc, Alpha etc) how long GNU/Linux will really suspends
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executing the utility.
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<p>
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The program speed downgrade at the development machine that mball needed was
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3 times the original exection time, while system loading stayed under 30%.
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At that time the development machine is an 486DX2-66 with a Seagate ST32151N
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SCSI harddisk.
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<p>
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The extra usleep code is only active if you run these utils with the -quiet
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switch and when this is set in mbsetup. See menu 1->5.
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With this switch, the program is mostly run by cron. If you onmit
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this switch, this is probably when you start the program manually, it will
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then always run at full speed, no matter what the setting in mbsetup is.
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<p>
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If you have a fast system or don't care that the performance of your system
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drops because of background processing, you can turn this future off with
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mbsetup in the global section. (menu 1->5).
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<p>
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Remember, if you have a PII-400 MMX or so with IDE disks, you may still have
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performance problems and need to set that switch to yes. There is only one
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way to find out if you need it.
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<p>
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Well, actually, I tested this on a Dell Latitude PII-266, setting the switch to
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yes gave better performance then no. Why? The CPU has more time for the slow
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IDE disk. With the slow switch on programs runs even faster then with the switch
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off. Modern hardware (PIII and later) may run fine with the slow switch turned
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off.
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<p>
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In januari 2004 the usleep code is replaced by a milliseconds timer written
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around the nanosleep system call. This call conforms to POSIX.1b and is written
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so that if the timer is interrupted it will resume with the time left to do.
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The real minimum time the timer runs is 10 ms on Intel systems, see also <b>man
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nanosleep</b> All usleep(1) calls are now msleep(1) calls, in practice these are
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pauses of 10 ms.
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<P>
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Michiel.
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<p>
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