On Alpha we have spinlocks that are 32b in size and an efficient
cmpxchg64 implementation, so we qualify to make use of cmpxchg backed
lockrefs. Select the ARCH_USE_CMPXCHG_LOCKREF Kconfig symbol and provide
a trivial implementation of arch_spin_value_unlocked to satisfy the
lockref code.
Using Linus' simple testcase from
http://article.gmane.org/gmane.linux.file-systems/77466 on a dual CPU
ES47 system I see around an 8% gain:
N Min Max Median Avg Stddev
x 30 6194580 6295654 6272504 6272514 17694.232
+ 30 6731164 6786334 6767982 6764274 13738.863
Difference at 95.0% confidence
491760 +/- 8188.17
7.83992% +/- 0.130541%
(Student's t, pooled s = 15840.5)
Signed-off-by: Matt Turner <mattst88@gmail.com>
8f8dcb3f7f