Date: Wed, 22 Jan 2014 11:06:39 -0800 From: Alfred Perlstein <alfred@freebsd.org> To: John-Mark Gurney <jmg@funkthat.com>, 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: <52E016BF.80102@freebsd.org> In-Reply-To: <20140122181443.GU75135@funkthat.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> <20140122181443.GU75135@funkthat.com>
next in thread | previous in thread | raw e-mail | index | archive | help
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 <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. > 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
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?52E016BF.80102>