From owner-freebsd-current Sun Feb 17 12:25:46 2002 Delivered-To: freebsd-current@freebsd.org Received: from apollo.backplane.com (apollo.backplane.com [216.240.41.2]) by hub.freebsd.org (Postfix) with ESMTP id 9875337B405 for ; Sun, 17 Feb 2002 12:25:40 -0800 (PST) Received: (from dillon@localhost) by apollo.backplane.com (8.11.6/8.9.1) id g1HKPc589840; Sun, 17 Feb 2002 12:25:38 -0800 (PST) (envelope-from dillon) Date: Sun, 17 Feb 2002 12:25:38 -0800 (PST) From: Matthew Dillon Message-Id: <200202172025.g1HKPc589840@apollo.backplane.com> To: Bruce Evans Cc: Subject: Re: 'microuptime() went backwards ...' using ACPI timer. Shouldn't that be impossible? References: <20020217184436.M934-100000@gamplex.bde.org> Sender: owner-freebsd-current@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG Ok, I've looked at the code more carefully and I understand how this works now. However, it is not enough in an SMP environment. You need a generation count in the timecounter structure and you also need a synchronization point when you switch time counters or a process running on a different cpu may wind up using a time counter that is being actively updated. I'm experimenting with your patch now. I'll send email when I have some test results. -Matt : :I just wrote the following fix for some of the overflow problems. : :%%% :Index: kern_tc.c :=================================================================== :RCS file: /home/ncvs/src/sys/kern/kern_tc.c,v :retrieving revision 1.113 :diff -c -2 -r1.113 kern_tc.c :... To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message