Date: Wed, 04 Dec 2002 10:06:16 -0800 From: Terry Lambert <tlambert2@mindspring.com> To: Stijn Hoop <stijn@win.tue.nl> Cc: Mike Silbersack <silby@silby.com>, freebsd-hackers@freebsd.org Subject: Re: [nephtes@openface.ca: [Xmame] Use of usleep() with -sleepidle] Message-ID: <3DEE4418.868B4936@mindspring.com> References: <20021202151816.GJ83264@pcwin002.win.tue.nl> <20021202114019.R31106-100000@patrocles.silby.com> <20021204113154.GA205@pcwin002.win.tue.nl>
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Stijn Hoop wrote: > On Mon, Dec 02, 2002 at 11:49:03AM -0600, Mike Silbersack wrote: > > The time select() takes should be directly related to your system's hz > > setting. The default for FreeBSD is 100, which means that the interrupt > > timer will fire every 10ms. If you want to play with that, edit > > /etc/sysctl.conf and set kern.hz="1000", which should give you 1 ms > > accuracy. > > With the mentioned change of /etc/sysctl.conf to /boot/loader.conf, I am > indeed seeing much better times on this 'benchmark'. See attached log. Not > only the _select_sleep method benefits from this. What are the reasons *not* > to do this? Increased context switch overhead. > > As to why Linux may appear "better"... I believe that Linux defaults to > > hz=100, but that the default switched to hz=1000 sometime in the recent > > past. > > And why don't we do the same? (I suspect this is related to the question > above :) Increased context switch overhead. > > To answer your final question: Sleep accuracy doesn't matter to most > > applications, but I'm sure counterexamples could be found. > > Such as emulators :) Actually, for the case you are talking about, your emulator should be using aggregate instead of discrete timeouts, and you would not be having a problem. It's not useful to do 100 1ms timeouts to achieve a 100ms timeout, when you can ask for a single 100ms timeout. I would count this as a bug in your emulator. -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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