Date: Wed, 22 Jan 2014 10:14:43 -0800 From: John-Mark Gurney <jmg@funkthat.com> To: Scott Long <scott4long@yahoo.com> Cc: src-committers@FreeBSD.org, Neel Natu <neel@FreeBSD.org>, John Baldwin <jhb@FreeBSD.org>, svn-src-all@FreeBSD.org, Rui Paulo <rpaulo@felyko.com>, svn-src-head@FreeBSD.org, Alexander Kabaev <kabaev@gmail.com> Subject: Re: svn commit: r260898 - head/sys/kern Message-ID: <20140122181443.GU75135@funkthat.com> In-Reply-To: <D04BF613-A78D-43B8-A22B-DA8F72D22430@yahoo.com> References: <201401200159.s0K1xa5X012123@svn.freebsd.org> <1536225.gsjt6oXMt2@pippin.baldwin.cx> <20140120171844.69e065fb@kan.dyndns.org> <201401211126.18930.jhb@freebsd.org> <D04BF613-A78D-43B8-A22B-DA8F72D22430@yahoo.com>
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Scott Long wrote this message on Tue, Jan 21, 2014 at 15:12 -0700: > On Jan 21, 2014, at 9:26 AM, John Baldwin <jhb@freebsd.org> wrote: > > > On Monday, January 20, 2014 5:18:44 pm Alexander Kabaev wrote: > >> On Mon, 20 Jan 2014 11:32:29 -0500 > >> John Baldwin <jhb@freebsd.org> wrote: > >> > >>> On Sunday 19 January 2014 18:18:03 Rui Paulo wrote: > >>>> On 19 Jan 2014, at 17:59, Neel Natu <neel@FreeBSD.org> 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 <CONSTANT1> + <CONSTANT2> * 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. -- John-Mark Gurney Voice: +1 415 225 5579 "All that I will do, has been done, All that I have, has not."
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