tree 77f3b85e0f59a168ac78639e510ebcbd3791b3d2
parent 4c75f84f2c781beb230031234ed961d28771a764
author Paul Mackerras <paulus@samba.org> 1244841005 +0000
committer Benjamin Herrenschmidt <benh@kernel.crashing.org> 1245036458 +1000

lib: Provide generic atomic64_t implementation

Many processor architectures have no 64-bit atomic instructions, but
we need atomic64_t in order to support the perf_counter subsystem.

This adds an implementation of 64-bit atomic operations using hashed
spinlocks to provide atomicity.  For each atomic operation, the address
of the atomic64_t variable is hashed to an index into an array of 16
spinlocks.  That spinlock is taken (with interrupts disabled) around the
operation, which can then be coded non-atomically within the lock.

On UP, all the spinlock manipulation goes away and we simply disable
interrupts around each operation.  In fact gcc eliminates the whole
atomic64_lock variable as well.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>