Date: Wed, 30 Jan 2008 15:55:49 +0100 From: Ivan Voras <ivoras@freebsd.org> To: freebsd-stable@freebsd.org Subject: Re: option HZ=? Message-ID: <fnq359$gjc$1@ger.gmane.org> In-Reply-To: <20080130140711.GA19047@epia-2.farid-hajji.net> References: <47A073C2.1060209@moneybookers.com> <20080130140711.GA19047@epia-2.farid-hajji.net>
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cpghost wrote: > 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. Isn't there also something bad about TCP timestamp overflow?
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