From owner-freebsd-hackers Wed Aug 22 21:55:55 2001 Delivered-To: freebsd-hackers@freebsd.org Received: from iguana.aciri.org (iguana.aciri.org [192.150.187.36]) by hub.freebsd.org (Postfix) with ESMTP id 03DD037B407 for ; Wed, 22 Aug 2001 21:55:53 -0700 (PDT) (envelope-from rizzo@iguana.aciri.org) Received: (from rizzo@localhost) by iguana.aciri.org (8.11.3/8.11.1) id f7N4rQi52619; Wed, 22 Aug 2001 21:53:26 -0700 (PDT) (envelope-from rizzo) From: Luigi Rizzo Message-Id: <200108230453.f7N4rQi52619@iguana.aciri.org> Subject: Re: clock synchronization quality via NTP ? In-Reply-To: <200108230449.f7N4n6W81268@harmony.village.org> from Warner Losh at "Aug 22, 2001 10:49: 6 pm" To: imp@harmony.village.org (Warner Losh) Date: Wed, 22 Aug 2001 21:53:26 -0700 (PDT) Cc: phk@critter.freebsd.dk, thierry@herbelot.com, hackers@FreeBSD.ORG, peo@sssup.it X-Mailer: ELM [version 2.4ME+ PL43 (25)] MIME-Version: 1.0 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 > beyond "normal HVAC" and stock xtals on the motherboard. This is > after we've done the fast interrupt hack. Without it, the other > system activity was causing enough interrupt latncy variance that we > would see more like +- 80us with outliers way off in the weeds > (+- just under 10ms!). Warner, this sounds related to a problem we are having... a student of mine is seeing sporadic but relatively large (~50-100us) variations in the period of clock interrupts (int0 calls to the assembly routine). This is in the assembler part of the interrupt service routine, so the only reason I can see for these variations is that there are some significantly large sections of code (this is a 750 MHz box) which run with interrupts disable on the CPU. Is this the case ? And if so, what is the "fast interrupt hack" that you are mentioning and how would it improve things ? thanks luigi ----------------------------------+----------------------------------------- Luigi RIZZO, luigi@iet.unipi.it . ACIRI/ICSI (on leave from Univ. di Pisa) http://www.iet.unipi.it/~luigi/ . 1947 Center St, Berkeley CA 94704 Phone: (510) 666 2927 ----------------------------------+----------------------------------------- To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message