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parisc: Remove unnecessary barriers from spinlock.h

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Now that mb() is an instruction barrier, it will slow performance if we issue
unnecessary barriers.

The spinlock defines have a number of unnecessary barriers.  The __ldcw()
define is both a hardware and compiler barrier.  The mb() barriers in the
routines using __ldcw() serve no purpose.

The only barrier needed is the one in arch_spin_unlock().  We need to ensure
all accesses are complete prior to releasing the lock.

Signed-off-by: John David Anglin <dave.anglin@bell.net>
Cc: stable@vger.kernel.org # 4.0+
Signed-off-by: Helge Deller <deller@gmx.de>
This commit is contained in:
John David Anglin
2018-08-12 16:31:17 -04:00
committed by Helge Deller
parent 7797167ffd
commit 3b885ac1dc
1 changed files with 2 additions and 6 deletions
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8
arch/parisc/include/asm/spinlock.h
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@@ -20,7 +20,6 @@ static inline void arch_spin_lock_flags(arch_spinlock_t *x,
{ {
volatile unsigned int *a; volatile unsigned int *a;
mb();
a = __ldcw_align(x); a = __ldcw_align(x);
while (__ldcw(a) == 0) while (__ldcw(a) == 0)
while (*a == 0) while (*a == 0)
@@ -30,17 +29,16 @@ static inline void arch_spin_lock_flags(arch_spinlock_t *x,
local_irq_disable(); local_irq_disable();
} else } else
cpu_relax(); cpu_relax();
mb();
} }
#define arch_spin_lock_flags arch_spin_lock_flags #define arch_spin_lock_flags arch_spin_lock_flags
static inline void arch_spin_unlock(arch_spinlock_t *x) static inline void arch_spin_unlock(arch_spinlock_t *x)
{ {
volatile unsigned int *a; volatile unsigned int *a;
mb();
a = __ldcw_align(x); a = __ldcw_align(x);
*a = 1;
mb(); mb();
*a = 1;
} }
static inline int arch_spin_trylock(arch_spinlock_t *x) static inline int arch_spin_trylock(arch_spinlock_t *x)
@@ -48,10 +46,8 @@ static inline int arch_spin_trylock(arch_spinlock_t *x)
volatile unsigned int *a; volatile unsigned int *a;
int ret; int ret;
mb();
a = __ldcw_align(x); a = __ldcw_align(x);
ret = __ldcw(a) != 0; ret = __ldcw(a) != 0;
mb();
return ret; return ret;
} }