powerpc: Add support for the optimised lockref implementation
This commit adds the architecture support required to enable the
optimised implementation of lockrefs.
That's as simple as defining arch_spin_value_unlocked() and selecting
the Kconfig option.
We also define cmpxchg64_relaxed(), because the lockref code does not
need the cmpxchg to have barrier semantics.
Using Linus' test case[1] on one system I see a 4x improvement for the
basic enablement, and a further 1.3x for cmpxchg64_relaxed(), for a
total of 5.3x vs the baseline.
On another system I see more like 2x improvement.
[1]: http://marc.info/?l=linux-fsdevel&m=137782380714721&w=4
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/include/asm/spinlock.h b/arch/powerpc/include/asm/spinlock.h
index 5f54a74..5162f8c 100644
--- a/arch/powerpc/include/asm/spinlock.h
+++ b/arch/powerpc/include/asm/spinlock.h
@@ -54,6 +54,11 @@
#define SYNC_IO
#endif
+static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
+{
+ return lock.slock == 0;
+}
+
/*
* This returns the old value in the lock, so we succeeded
* in getting the lock if the return value is 0.