From owner-freebsd-hackers Thu Jan 31 14:14: 8 2002 Delivered-To: freebsd-hackers@freebsd.org Received: from herbelot.dyndns.org (d211.dhcp212-198-26.noos.fr [212.198.26.211]) by hub.freebsd.org (Postfix) with ESMTP id 316C037B416 for ; Thu, 31 Jan 2002 14:14:03 -0800 (PST) Received: from herbelot.com (tulipe.herbelot.nom [192.168.1.5]) by herbelot.dyndns.org (8.9.3/8.9.3) with ESMTP id XAA06935; Thu, 31 Jan 2002 23:13:44 +0100 (CET) (envelope-from thierry@herbelot.com) Message-ID: <3C59C198.78EDFEA9@herbelot.com> Date: Thu, 31 Jan 2002 23:13:44 +0100 From: Thierry Herbelot X-Mailer: Mozilla 4.79 [en] (X11; U; Linux 2.4.2 i386) X-Accept-Language: en MIME-Version: 1.0 To: Eugene Panchenko Cc: hackers@FreeBSD.ORG Subject: Re: Clock Granularity (kernel option HZ) References: Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG I've used a large collection of PCs running somewhat real-time network analysis with a HZ set at 5000Hz with absolutely no ill effects (this was with P-III-450's) using HZ=10000 was outside of the possibilities of the machines. one big gain is with timing, which will be better (I myself used NTP to have a coherent timing on the collection of PC's, with an inter-correlation better than 1 ms) TfH Eugene Panchenko wrote: > > Hello! > > I've seen various postings on the Net where people reported > network-related and overall performance improvements caused > by settig HZ kernel option to 1000 (for example), that is, > reducing a tick size to 1ms for their FreeBSD and Linux > systems. However, several problems seem to arise, such as > some device drivers do not include HZ in calculating their > timeout value, but simply assume HZ to be 100, and also some > utility programs such as top or ps take timing information > from the kernel in ticks, also assuming 10ms ticks, however, > most of these saying were related to Linux. How safe it is > to bump up HZ to, say, 1000 in FreeBSD (I use 4.5-STABLE)? > What pitfals will I encounter (drivers, top/ps)? Is there > are going to be [promised] performance increase? Do I > really need it? Thank you. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message