From owner-svn-src-head@FreeBSD.ORG Wed Jan 22 19:06:52 2014 Return-Path: Delivered-To: svn-src-head@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 3B3A6D5F; Wed, 22 Jan 2014 19:06:52 +0000 (UTC) Received: from elvis.mu.org (elvis.mu.org [192.203.228.196]) by mx1.freebsd.org (Postfix) with ESMTP id 16D47187F; Wed, 22 Jan 2014 19:06:51 +0000 (UTC) Received: from Alfreds-MacBook-Pro.local (unknown [50.204.88.5]) by elvis.mu.org (Postfix) with ESMTPSA id CCB4F1A3C4D; Wed, 22 Jan 2014 11:06:42 -0800 (PST) Message-ID: <52E016BF.80102@freebsd.org> Date: Wed, 22 Jan 2014 11:06:39 -0800 From: Alfred Perlstein Organization: FreeBSD User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: John-Mark Gurney , Scott Long Subject: Re: svn commit: r260898 - head/sys/kern References: <201401200159.s0K1xa5X012123@svn.freebsd.org> <1536225.gsjt6oXMt2@pippin.baldwin.cx> <20140120171844.69e065fb@kan.dyndns.org> <201401211126.18930.jhb@freebsd.org> <20140122181443.GU75135@funkthat.com> In-Reply-To: <20140122181443.GU75135@funkthat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: src-committers@FreeBSD.org, Neel Natu , John Baldwin , svn-src-all@FreeBSD.org, Rui Paulo , svn-src-head@FreeBSD.org, Alexander Kabaev X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.17 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 22 Jan 2014 19:06:52 -0000 On 1/22/14, 10:14 AM, John-Mark Gurney wrote: > Scott Long wrote this message on Tue, Jan 21, 2014 at 15:12 -0700: >> On Jan 21, 2014, at 9:26 AM, John Baldwin wrote: >> >>> On Monday, January 20, 2014 5:18:44 pm Alexander Kabaev wrote: >>>> On Mon, 20 Jan 2014 11:32:29 -0500 >>>> John Baldwin wrote: >>>> >>>>> On Sunday 19 January 2014 18:18:03 Rui Paulo wrote: >>>>>> On 19 Jan 2014, at 17:59, Neel Natu wrote: >>>>>>> Author: neel >>>>>>> Date: Mon Jan 20 01:59:35 2014 >>>>>>> New Revision: 260898 >>>>>>> URL: http://svnweb.freebsd.org/changeset/base/260898 >>>>>>> >>>>>>> Log: >>>>>>> Bump up WITNESS_COUNT from 1024 to 1536 so there are sufficient >>>>>>> entries for >>>>>>> WITNESS to actually work. >>>>>> This value should be automatically tuned... >>>>> How do you propose to do so? This is the count of locks initialized >>>>> before witness' own SYSINIT is executed and the array it sizes is >>>>> allocated statically at compile time. This used to not be a static >>>>> array, but an intrusive list embedded in locks themselves, but we >>>>> decided to shave a pointer off of each lock that was only used for >>>>> that and to use a statically sized table instead. >>>>> >>>>> -- >>>>> John Baldwin >>>> As + * MAXCPU, as evidently most recent >>>> overflows reported were caused by jacking MAXCPU up from its default >>>> value? >>> If raising MAXCPU changes the number of unique lock names used, then the >>> locks are named incorrectly. We don't use the 'pid' in the name for >>> PROC_LOCK precisely so that WITNESS will treat them all the same so >>> that if if it learns a lock order for pid 37 it enforces the same lock >>> order for pid 38. Device locks should follow a similar rule. They >>> should generally not include the device name (and in some cases they >>> really shouldn't even have the driver name). >> Why shouldn?t they have a driver and device name? Wouldn?t it help identify >> possible deadlocks from driver instances calling into each other? > Locks have a name and a type. The type is used for witness, but if it > is NULL, the name is used. So you could if you wanted, create a common > type, and then put driver/device name in name, but the passed in strings > to both name and type have to be stable storage (only the pointer is > stored), so you can't use a stack variable to construct it. > Hmm, what if locks had a pointer to a 2 element char * array, the first being the name, the second the type. That would keep the size of the lock down and most locks could share a common tuple of name/type in each subsystem. This would allow us to get rid of the pending static list. effectively: struct lock_object { char *lo_name; /* Individual lock name. */ u_int lo_flags; u_int lo_data; /* General class specific data. */ struct witness *lo_witness; /* Data for witness. */ }; would change to: struct lock_object { char **lo_name_type; /* Individual lock name[0]/type[1]. */ u_int lo_flags; u_int lo_data; /* General class specific data. */ struct witness *lo_witness; /* Data for witness. */ }; This may be somewhat disruptive, I haven't played with how it would actually change driver/etc/code. -Alfred