alpha: select CONFIG_ARCH_USE_CMPXCHG_LOCKREF.

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>
This commit is contained in:
Matt Turner 2015-08-04 14:35:05 -07:00
parent 64291f7db5
commit 8f8dcb3f7f
2 changed files with 6 additions and 0 deletions

View file

@ -3,6 +3,7 @@ config ALPHA
default y
select ARCH_MIGHT_HAVE_PC_PARPORT
select ARCH_MIGHT_HAVE_PC_SERIO
select ARCH_USE_CMPXCHG_LOCKREF
select HAVE_AOUT
select HAVE_IDE
select HAVE_OPROFILE

View file

@ -16,6 +16,11 @@
#define arch_spin_unlock_wait(x) \
do { cpu_relax(); } while ((x)->lock)
static inline int arch_spin_value_unlocked(arch_spinlock_t lock)
{
return lock.lock == 0;
}
static inline void arch_spin_unlock(arch_spinlock_t * lock)
{
mb();