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>
diff --git a/lib/Makefile b/lib/Makefile
index 34c5c0e..8e9bcf9 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -95,6 +95,8 @@
obj-$(CONFIG_GENERIC_CSUM) += checksum.o
+obj-$(CONFIG_GENERIC_ATOMIC64) += atomic64.o
+
hostprogs-y := gen_crc32table
clean-files := crc32table.h