On 11/14/2014 09:12 AM, Iain Sandoe wrote: > my locks are only 4 bytes [whereas they are > rounded-up-to-n-cachlines(sizeof(pthreads mutext)) for the posix > implementation]. > The items that they are locking are of arbitrary size (at least up to one > page). > > hmmm .. there's something I'm not following about what you are seeing as a > problem here. > > In the posix implementation the granularity calculation is also used to > round up the space allocated in the locks table for each pthreads mutex > (i.e. it has two uses, AFAICT).
No, there's only one use: How large an area is *protected* by the lock. Since we need to protect one page of these areas, we need NLOCKS = PAGE_SIZE / WATCH_SIZE locks, which are then allocated in an array. We do not care how large that array is. So if you'd like to differ from the posix implementation in protecting 4 bytes at a time, rather than one cacheline at a time, then just change WATCH_SIZE to 4. The fact that WATCH_SIZE happens to equal to the lock size is simply a coincidence. r~
