From owner-cvs-src@FreeBSD.ORG Tue Jul 25 20:26:58 2006 Return-Path: X-Original-To: cvs-src@FreeBSD.org Delivered-To: cvs-src@FreeBSD.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id D4ED716A4DA; Tue, 25 Jul 2006 20:26:58 +0000 (UTC) (envelope-from phk@phk.freebsd.dk) Received: from phk.freebsd.dk (phk.freebsd.dk [130.225.244.222]) by mx1.FreeBSD.org (Postfix) with ESMTP id 7548443D46; Tue, 25 Jul 2006 20:26:58 +0000 (GMT) (envelope-from phk@phk.freebsd.dk) Received: from critter.freebsd.dk (critter.freebsd.dk [192.168.48.2]) by phk.freebsd.dk (Postfix) with ESMTP id D809E170C5; Tue, 25 Jul 2006 20:26:55 +0000 (UTC) To: David Malone From: "Poul-Henning Kamp" In-Reply-To: Your message of "Tue, 25 Jul 2006 21:23:11 +0100." <200607252123.aa75409@salmon.maths.tcd.ie> Date: Tue, 25 Jul 2006 20:26:54 +0000 Message-ID: <11936.1153859214@critter.freebsd.dk> Cc: src-committers@FreeBSD.org, cvs-src@FreeBSD.org, "Christian S.J. Peron" , cvs-all@FreeBSD.org, Sam Leffler , Jung-uk Kim Subject: Re: cvs commit: src/sys/net bpf.c X-BeenThere: cvs-src@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: CVS commit messages for the src tree List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 25 Jul 2006 20:26:59 -0000 In message <200607252123.aa75409@salmon.maths.tcd.ie>, David Malone writes: >> I'm not sure I know what you mean by "trivial timecounter", but the >> only reason we don't have a way to deregister a timecounter yet is >> that so far I'm probably the only one who have ever need it :-) > >I was thinking about this recently too actually, as I was going to >see how good the 64 bit counter on ath cards was in comparison to >other things that were available. The first gottcha to look out for is upper/lower half rollover issues, if you read it as two 32 bit registers: you need to check if the lower part rolled over without the upper part getting updated, or the more pathological case: the upper part being updated before the lower part rolled voer. 32 bits is quite likely to be enough for a timecounter so that may not even be an issue. Next is the matter of the crystal that drives it, the temperature stability of that xtal etc etc. >other things that were available. I'm not sure how much complexity >a timecounter that could vanish at any moment would introduce - I >didn't get that far yet. It's not too bad, we can switch pretty quickly. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.