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Michiel Broek
2004-01-25 10:57:35 +00:00
parent 1382701bd8
commit 5a0e317f23
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<PRE>
usleep.doc
<BLOCKQUOTE>
<div align='right'><h5>Last update 23-Jan-2004</h5></div>
<div align='center'><H1>System load and the usleep() call.</H1></div>
At some time when developping MBSE BBS I decided that background utilities
did't need full speed to do their jobs. BBS utilities under DOS needed
to run as fast as possible because you needed to bring the bbs down to run
these programs and users couldn't login during that time.
<p>
Starting with mball, the allfiles creator, I inserted code that does usleep(1)
after each 5 processed files. The 1 microsecond is not really the time the
program pauses, it's probably a lot longer. I think this depends on the
hardware type, (Intel, Sparc, Alpha etc) how long GNU/Linux will really suspends
executing the utility.
<p>
The program speed downgrade at the development machine that mball needed was
3 times the original exection time, while system loading stayed under 30%.
At that time the development machine is an 486DX2-66 with a Seagate ST32151N
SCSI harddisk.
<p>
The extra usleep code is only active if you run these utils with the -quiet
switch and when this is set in mbsetup. See menu 1-&gt;5.
With this switch, the program is mostly run by cron. If you onmit
this switch, this is probably when you start the program manually, it will
then always run at full speed, no matter what the setting in mbsetup is.
<p>
If you have a fast system or don't care that the performance of your system
drops because of background processing, you can turn this future off with
mbsetup in the global section. (menu 1-&gt;5).
<p>
Remember, if you have a PII-400 MMX or so with IDE disks, you may still have
performance problems and need to set that switch to yes. There is only one
way to find out if you need it.
<p>
Well, actually, I tested this on a Dell Latitude PII-266, setting the switch to
yes gave better performance then no. Why? The CPU has more time for the slow
IDE disk. With the slow switch on programs runs even faster then with the switch
off.
off. Modern hardware (PIII and later) may run fine with the slow switch turned
off.
<p>
In januari 2004 the usleep code is replaced by a milliseconds timer written
around the nanosleep system call. This call conforms to POSIX.1b and is written
so that if the timer is interrupted it will resume with the time left to do.
The real minimum time the timer runs is 10 ms on Intel systems, see also <b>man
nanosleep</b> All usleep(1) calls are now msleep(1) calls, in practice these are
pauses of 10 ms.
<P>
Michiel.
</PRE>
<p>
<A HREF="index.htm"><IMG SRC="../images/b_arrow.png" ALT="Back" Border="0">Go Back</A>
</BLOCKQUOTE>
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