On Tuesday, January 21, 2014 5:12:30 pm Scott Long wrote: > > On Jan 21, 2014, at 9:26 AM, John Baldwin <j...@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 <j...@freebsd.org> wrote: > >> > >>> On Sunday 19 January 2014 18:18:03 Rui Paulo wrote: > >>>> On 19 Jan 2014, at 17:59, Neel Natu <n...@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?
It prevents that. Let's say you have twe0 and twe1 and you use 'twe0 I/O' and 'twe1 I/O' for the locks. If you lock 'twe1 I/O' after 'twe0 I/O' WITNESS will happily just create a new known lock order and not complain. It will only complain if later during the same uptime you later acquire 'twe0 I/O' after 'twe1 I/O'. If instead you name the lock 'twe I/O', then the first time you try to acquire a second 'twe I/O' lock, WITNESS will complain (and in general drivers shouldn't be calling into each other, so we want them to complain the first time). This is why we have the MTX_NETWORK_LOCK hack for driver transmit ring locks, so that WITNESS uses a single set of lock order relationships between transmit ring locks and other locks. -- John Baldwin _______________________________________________ svn-src-head@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
