atomic_ops vs mutex

[raymond.meyer%rambler.ru@localhost]

The following is from the atomic_ops(3) man page:

Performance
Because atomic memory operations require expensive
synchronization at the hardware level, applications should take care to
minimize their use.  In certain cases, it may be more appropriate to
use a mutex, especially if more than one memory location will be
modified.

I have two questions:

1. Are all atomic_ops functions, or some of them macros?

2. In what cases would it be better to use atomic_ops, instead of
locking and unlocking mutex?