Re: Dynamically allocated locks

[Matt Thomas <matt%3am-software.com@localhost>]

On Mar 23, 2008, at 10:52 AM, Andrew Doran wrote:

> Hi,
>
> This patch allows for dynamically allocated locks.
>
> http://www.netbsd.org/~ad/lockobj.diff
>
> Each lock gets its own cache line, which can reduce cache coherency  
> costs
> when the lock is very active. The locks are reference counted so  
> can be
> shared between objects. That could be used for the two ends of a  
> Unix socket
> connection, or to share a lock between clone()d processes in order to
> protect common state like signal actions, etc.
>
> Any objections?

Yes.  One / cacheline size is a dramatic waste of space.  Some  
systems have
128 bytes per cacheline.  On systems with small caches or UP systems  
it's
extremely expensive.

Other than that its fine.  I can see not crossing a cacheline boundary,
but only 1 / cacheline is just wrong.