Came across the following in a paper from Oct 2010. Was wondering is this is old news I missed in this group. http://pdos.csail.mit.edu/papers/linux:osdi10.pdf about Linux optimization on multi-core CPU's.
The group at MIT were exploring how some Linux apps were scaling up --- sometimes badly, mostly due to hidden contention over cache-line consistency across the cores' caches. In a nutshell: if an app, or the system calls it uses, tries to modify anything in a cache line (32-64 byte slice of memory) that another core is using, there's a lot of fumbling in the dark to make sure there is no conflict. When I saw PostgreSQL named in the abstract, I thought, "Aha! Contention over shm". Not so. Skip to page 11 (section 5.5) for most of the PG specifics.
