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bit_spinlock: don't play preemption games inside the busy loop

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When we are waiting for the bit-lock to be released, and are looping
over the 'cpu_relax()' should not be doing anything else - otherwise we
miss the point of trying to do the whole 'cpu_relax()'.

Do the preemption enable/disable around the loop, rather than inside of
it.

Noticed when I was looking at the code generation for the dcache
__d_drop usage, and the code just looked very odd.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2011-04-25 18:10:58 -07:00
parent 5dd12af05c
commit 3dd2ee4824
1 changed files with 4 additions and 4 deletions
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8
include/linux/bit_spinlock.h
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@ -23,11 +23,11 @@ static inline void bit_spin_lock(int bitnum, unsigned long *addr)
preempt_disable(); preempt_disable();
#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK) #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
while (unlikely(test_and_set_bit_lock(bitnum, addr))) { while (unlikely(test_and_set_bit_lock(bitnum, addr))) {
while (test_bit(bitnum, addr)) { preempt_enable();
preempt_enable(); do {
cpu_relax(); cpu_relax();
preempt_disable(); } while (test_bit(bitnum, addr));
} preempt_disable();
} }
#endif #endif
__acquire(bitlock); __acquire(bitlock);