From owner-freebsd-hackers@FreeBSD.ORG Fri Oct 20 12:47:37 2006 Return-Path: X-Original-To: freebsd-hackers@freebsd.org Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id E05C016A403 for ; Fri, 20 Oct 2006 12:47:37 +0000 (UTC) (envelope-from rwatson@FreeBSD.org) Received: from cyrus.watson.org (cyrus.watson.org [209.31.154.42]) by mx1.FreeBSD.org (Postfix) with ESMTP id 7A7C643D4C for ; Fri, 20 Oct 2006 12:47:37 +0000 (GMT) (envelope-from rwatson@FreeBSD.org) Received: from fledge.watson.org (fledge.watson.org [209.31.154.41]) by cyrus.watson.org (Postfix) with ESMTP id 185F046DA6; Fri, 20 Oct 2006 08:47:37 -0400 (EDT) Date: Fri, 20 Oct 2006 13:47:37 +0100 (BST) From: Robert Watson X-X-Sender: robert@fledge.watson.org To: Karl Pielorz In-Reply-To: <82C14B40C9061504218D7585@Unsupported> Message-ID: <20061020134552.H38852@fledge.watson.org> References: <20061020110151.GU55428@deviant.kiev.zoral.com.ua> <82C14B40C9061504218D7585@Unsupported> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Cc: Kostik Belousov , freebsd-hackers@freebsd.org Subject: Re: 6.1-STABLE hangs, ddb shows 'acpi_timer_read'? X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 20 Oct 2006 12:47:38 -0000 On Fri, 20 Oct 2006, Karl Pielorz wrote: >> On Fri, Oct 20, 2006 at 11:56:33AM +0100, Karl Pielorz wrote: >>> >>> I have a crash dump from it - which I've saved (I'm moderately familiar >>> with working with dumps, but this one is split into two?) >>> >>> If anyone has any pointers, or can do some hand holding to get more info >>> from the dump, or what to do next time it happens? >> >> See >> http://www.freebsd.org/doc/en_US.ISO8859-1/books/developers-handbook/kern >> eldebug-deadlocks.html > > Thanks for the link! Anyone know much is all that lot (such as > INVARIANTS/WITNESS) etc. likely to slow the machine down? - A few percent? > More? > > I'm just a little hesitant to put it all in, and end up with a machine > that's 80% slower :( Depends a lot on your workload. WITNESS used to really, really slow things down for kernel lock intensive workloads (VFS especially); now it just really slows things down. INVARIANTS overhead is generally measurable, but for most workloads it is likely <20%. The place INVARIANTS hits you is when the kernel is allocating and freeing lots of memory, during which INVARIANTS will be scrubbing and checking for use after free, etc. It's worth running with WITNESS when debugging deadlocks if possible, because it is, essentially, a deadlock debugging tool. A moderate number of people run with INVARIANTS in production, but you generally don't want to do that with WITNESS. Robert N M Watson Computer Laboratory University of Cambridge