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Commit 3405d230 authored by Michael Ellerman's avatar Michael Ellerman Committed by Benjamin Herrenschmidt
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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: default avatarMichael Ellerman <mpe@ellerman.id.au>
Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
parent f7d98d18

arch/powerpc/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -139,6 +139,7 @@ config PPC 
	select OLD_SIGACTION if PPC32

	select HAVE_DEBUG_STACKOVERFLOW

	select HAVE_IRQ_EXIT_ON_IRQ_STACK

	select ARCH_USE_CMPXCHG_LOCKREF if PPC64



config GENERIC_CSUM

	def_bool CPU_LITTLE_ENDIAN

arch/powerpc/include/asm/cmpxchg.h

+1 −0
Original line number Diff line number Diff line
@@ -300,6 +300,7 @@ __cmpxchg_local(volatile void *ptr, unsigned long old, unsigned long new, 
	BUILD_BUG_ON(sizeof(*(ptr)) != 8);				\

	cmpxchg_local((ptr), (o), (n));					\

  })

#define cmpxchg64_relaxed	cmpxchg64_local

#else

#include <asm-generic/cmpxchg-local.h>

#define cmpxchg64_local(ptr, o, n) __cmpxchg64_local_generic((ptr), (o), (n))

arch/powerpc/include/asm/spinlock.h

+5 −0
Original line number Diff line number Diff line
@@ -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.