Date: Wed, 30 Jan 2008 07:07:11 -0700 From: cpghost <cpghost@cordula.ws> To: Stefan Lambrev <stefan.lambrev@moneybookers.com> Cc: FreeBSD Stable <freebsd-stable@freebsd.org> Subject: Re: option HZ=? Message-ID: <20080130140711.GA19047@epia-2.farid-hajji.net> In-Reply-To: <47A073C2.1060209@moneybookers.com> References: <47A073C2.1060209@moneybookers.com>
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On Wed, Jan 30, 2008 at 02:55:30PM +0200, Stefan Lambrev wrote: > Greetings, > > I want to know what is the bad effect of increasing HZ too much? > And when is too much? What problems can I expect when HZ>2000? > Can I change this value without pre-compiling the kernel? You can change HZ by adding a line to /boot/loader.conf like this: kern.hz="100" (it works on RELENG_6 and RELENG_7 and I'm using this conservative setting on all my boxes, since I don't need faster context switching) If you set HZ too high, the kernel will spend too much overhead on unnecessary context switching, and it may even reach a point (with very high values of HZ) where interrupt service routines get interrupted way too often by clock ticks; i.e. interrupts would eventually come in faster than the kernel can service them. > Because all docs I found for HZ is in src/sys/conf/NOTES and it doesn't say > much. -cpghost. -- Cordula's Web. http://www.cordula.ws/
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