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/Kconfig b/lib/Kconfig
index 9960be0..bb1326d 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -194,4 +194,10 @@
config NLATTR
bool
+#
+# Generic 64-bit atomic support is selected if needed
+#
+config GENERIC_ATOMIC64
+ bool
+
endmenu