Messages in this thread |  | | Date | Wed, 13 Jul 2016 22:17:54 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 1/5] lockdep: Implement bitlock map allocator |
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On Mon, Jul 04, 2016 at 04:29:25PM +0900, Byungchul Park wrote: > On Fri, Jul 01, 2016 at 09:53:12AM +0200, Peter Zijlstra wrote: > > On Fri, Jul 01, 2016 at 09:24:44AM +0900, Byungchul Park wrote: > > > On Thu, Jun 30, 2016 at 02:59:19PM +0200, Peter Zijlstra wrote: > > > > On Mon, Jun 20, 2016 at 01:55:11PM +0900, Byungchul Park wrote: > > > > > > > > > +struct bitlock_map { > > > > > + struct hlist_node hash_entry; > > > > > + unsigned long bitaddr; /* ID */ > > > > > + struct lockdep_map map; > > > > > + int ref; /* reference count */ > > > > > +}; > > > > > > > > So this is effectively bigger than just adding a struct lockdep_map into > > > > whatever structure holds the bit spinlock to begin with. > > > > > > > > What is the gain? > > > > > > 1. I don't want to make being aware of lockdep essential to user of > > > bit-base lock, like spin lock, mutex, semaphore ans so on. In other > > > words, I want to make it work transparently. > > > > I want to discourage the use of bitlocks, they stink. > > I agree it has some problems. But someone who are sensive to memory > consumption still need to use bit-based lock. Right? > > I can stop this proposal because it's meaningless if bit-based lock can be > removed entirely since any requirement for bit-based lock does not exist > at all. But IMHO, it's worthy if the requirement be. > > > bitlocks must by their constraint be a test-and-set lock, with all the > > known problems those have. It also means they're a royal pain for -rt. > > I also think it's better to use rather spinlock in most cases unless memory > consumption is critical problem. But in the case memory consumption is > critical... what can we do?
So RT is already patching a whole bunch of bit-spinlocks into proper spinlocks, I would much rather we do that and get lockdep coverage that way.
That is, have the bit-spinlock for 'normal' kernels and use the proper spinlock for LOCKDEP || PREEMPT_RT kernels.
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