From owner-freebsd-stable@FreeBSD.ORG Wed Jan 30 14:24:09 2008 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 20B6616A46B for ; Wed, 30 Jan 2008 14:24:09 +0000 (UTC) (envelope-from cpghost@cordula.ws) Received: from fw.farid-hajji.net (fw.farid-hajji.net [213.146.115.42]) by mx1.freebsd.org (Postfix) with ESMTP id BA3BF13C467 for ; Wed, 30 Jan 2008 14:24:08 +0000 (UTC) (envelope-from cpghost@cordula.ws) Received: from epia-2.farid-hajji.net (epia-2 [192.168.254.11]) by fw.farid-hajji.net (Postfix) with ESMTP id 1DCC9E0458; Wed, 30 Jan 2008 15:07:12 +0100 (CET) Date: Wed, 30 Jan 2008 07:07:11 -0700 From: cpghost To: Stefan Lambrev Message-ID: <20080130140711.GA19047@epia-2.farid-hajji.net> References: <47A073C2.1060209@moneybookers.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <47A073C2.1060209@moneybookers.com> User-Agent: Mutt/1.5.17 (2007-11-01) Cc: FreeBSD Stable Subject: Re: option HZ=? X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 30 Jan 2008 14:24:09 -0000 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/