From owner-freebsd-current Thu Mar 30 10: 3:52 2000 Delivered-To: freebsd-current@freebsd.org Received: from rover.village.org (rover.village.org [204.144.255.49]) by hub.freebsd.org (Postfix) with ESMTP id 918A937BE9C; Thu, 30 Mar 2000 10:03:37 -0800 (PST) (envelope-from imp@harmony.village.org) Received: from harmony.village.org (harmony.village.org [10.0.0.6]) by rover.village.org (8.9.3/8.9.3) with ESMTP id LAA69350; Thu, 30 Mar 2000 11:03:35 -0700 (MST) (envelope-from imp@harmony.village.org) Received: from harmony.village.org (localhost.village.org [127.0.0.1]) by harmony.village.org (8.9.3/8.8.3) with ESMTP id LAA25466; Thu, 30 Mar 2000 11:03:08 -0700 (MST) Message-Id: <200003301803.LAA25466@harmony.village.org> To: Matthew Dillon Subject: Re: SMP buildworld times / performance tests Cc: Poul-Henning Kamp , Bruce Evans , Mike Smith , freebsd-current@FreeBSD.ORG In-reply-to: Your message of "Thu, 30 Mar 2000 09:15:54 PST." <200003301715.JAA73702@apollo.backplane.com> References: <200003301715.JAA73702@apollo.backplane.com> <1274.954416252@critter.freebsd.dk> Date: Thu, 30 Mar 2000 11:03:08 -0700 From: Warner Losh Sender: owner-freebsd-current@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG In message <200003301715.JAA73702@apollo.backplane.com> Matthew Dillon writes: : The general problem with the timecounter is that not only is the hardware : indeterminant, but the timecounter structure itself is *NOT* MP safe, : at least not by my read of it. : : It also doesn't appear to be interrupt safe. If a microtime() or : getmicrotime() call is interrupted and the interrupting interrupt calls : microtime(), it can corrupt the data returned by the first guy and : even corrupt the structure. We've hacked the parallel port interrupt to be a fast one on one of our boxes. It is connected to the pps driver which calls getnanotime to timestamp the pps pulse that came in. We've seen, in carefully plotting ntp data, that there are often (1 in a thousand) large dropouts in the times reported. They are in the neighborhood of the clock tick. Since ntp discards the outliers, this was a low priority issue for us given the overall nature of that particular system. At the time I took a look at it, and couldn't see how access to the counter could be mp safe, but didn't have a lot of time to pursue it. Warner To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message