svn commit: r209119 - head/sys/sys

[Robert N. M. Watson]

On 9 Jul 2010, at 19:58, Gabor PALI wrote:

>>  I assume there are reasonable alternatives that work around the
>> potential race with a small probability of a missed or extra update,
>> or similar, which would be fine.
> 
> In a few words: As far as I know, 64-bit atomic counters could be
> implemented by using cmpxchg8b or by a plain uint64_t variable protected
> by some kind of locking(9).

If we can do it in one atomic in the common case, and two atomics in an edge case, that sounds fine. I think any use of locking(9) would be sufficiently costly as to not be worth the improvements in consistency, given the frequency of statistics operations.

Robert