On Thu, Mar 22, 2012 at 09:59:01PM +0000, Keller, Jacob E wrote:

This means that readers don't block at all, and as long as the
readers don't conflict with each other, there is no contention or
writer starvation. It is possible for readers to 'live' lock, due to
a large number of write operations. However, the lock is designed
for few-writers, many readers. Which is what we have.

The readers do conflict with each other simply by reading the
registers E1000_SYSTIML and E1000_SYSTIMH. The locking is needed in
order to make these two reads "atomic."

Thanks,
Richard