Commit 8f8dcb3f authored Aug 04, 2015 by Matt Turner

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   6767982d   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>

parent 64291f7d

arch/alpha/Kconfig

+1 −0

Original line number	Diff line number	Diff line
		@@ -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

arch/alpha/include/asm/spinlock.h

+5 −0

Original line number	Diff line number	Diff line
		@@ -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();

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