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| author | Martin Schwidefsky <schwidefsky@de.ibm.com> | 2014-05-15 11:00:44 +0200 |
|---|---|---|
| committer | Martin Schwidefsky <schwidefsky@de.ibm.com> | 2014-05-20 08:58:53 +0200 |
| commit | bae8f567344a7cb6a23ca6e13096ba785c69eb42 (patch) | |
| tree | a0d91d9abf8405646ffbd5201d8c1b7f2627563c /arch/s390/lib | |
| parent | 2bf29df7460f4038f84ac5dea3cbe582d6d4af82 (diff) | |
| download | linux-bae8f567344a7cb6a23ca6e13096ba785c69eb42.tar.bz2 | |
s390/spinlock,rwlock: always to a load-and-test first
In case a lock is contended it is better to do a load-and-test first
before trying to get the lock with compare-and-swap. This helps to avoid
unnecessary cache invalidations of the cacheline for the lock if the
CPU has to wait for the lock. For an uncontended lock doing the
compare-and-swap directly is a bit better, if the CPU does not have the
cacheline in its cache yet the compare-and-swap will get it read-write
immediately while a load-and-test would get it read-only first.
Always to the load-and-test first to avoid the cacheline invalidations
for the contended case outweight the potential read-only to read-write
cacheline upgrade for the uncontended case.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Diffstat (limited to 'arch/s390/lib')
| -rw-r--r-- | arch/s390/lib/spinlock.c | 29 |
1 files changed, 16 insertions, 13 deletions
diff --git a/arch/s390/lib/spinlock.c b/arch/s390/lib/spinlock.c index 3f0e682b7e62..284d879a9b8c 100644 --- a/arch/s390/lib/spinlock.c +++ b/arch/s390/lib/spinlock.c @@ -100,12 +100,9 @@ int arch_spin_trylock_retry(arch_spinlock_t *lp) { int count; - for (count = spin_retry; count > 0; count--) { - if (arch_spin_is_locked(lp)) - continue; + for (count = spin_retry; count > 0; count--) if (arch_spin_trylock_once(lp)) return 1; - } return 0; } EXPORT_SYMBOL(arch_spin_trylock_retry); @@ -120,9 +117,9 @@ void _raw_read_lock_wait(arch_rwlock_t *rw) smp_yield(); count = spin_retry; } - if (!arch_read_can_lock(rw)) + old = ACCESS_ONCE(rw->lock); + if ((int) old < 0) continue; - old = rw->lock & 0x7fffffffU; if (_raw_compare_and_swap(&rw->lock, old, old + 1)) return; } @@ -140,9 +137,9 @@ void _raw_read_lock_wait_flags(arch_rwlock_t *rw, unsigned long flags) smp_yield(); count = spin_retry; } - if (!arch_read_can_lock(rw)) + old = ACCESS_ONCE(rw->lock); + if ((int) old < 0) continue; - old = rw->lock & 0x7fffffffU; local_irq_disable(); if (_raw_compare_and_swap(&rw->lock, old, old + 1)) return; @@ -156,9 +153,9 @@ int _raw_read_trylock_retry(arch_rwlock_t *rw) int count = spin_retry; while (count-- > 0) { - if (!arch_read_can_lock(rw)) + old = ACCESS_ONCE(rw->lock); + if ((int) old < 0) continue; - old = rw->lock & 0x7fffffffU; if (_raw_compare_and_swap(&rw->lock, old, old + 1)) return 1; } @@ -168,6 +165,7 @@ EXPORT_SYMBOL(_raw_read_trylock_retry); void _raw_write_lock_wait(arch_rwlock_t *rw) { + unsigned int old; int count = spin_retry; while (1) { @@ -175,7 +173,8 @@ void _raw_write_lock_wait(arch_rwlock_t *rw) smp_yield(); count = spin_retry; } - if (!arch_write_can_lock(rw)) + old = ACCESS_ONCE(rw->lock); + if (old) continue; if (_raw_compare_and_swap(&rw->lock, 0, 0x80000000)) return; @@ -185,6 +184,7 @@ EXPORT_SYMBOL(_raw_write_lock_wait); void _raw_write_lock_wait_flags(arch_rwlock_t *rw, unsigned long flags) { + unsigned int old; int count = spin_retry; local_irq_restore(flags); @@ -193,7 +193,8 @@ void _raw_write_lock_wait_flags(arch_rwlock_t *rw, unsigned long flags) smp_yield(); count = spin_retry; } - if (!arch_write_can_lock(rw)) + old = ACCESS_ONCE(rw->lock); + if (old) continue; local_irq_disable(); if (_raw_compare_and_swap(&rw->lock, 0, 0x80000000)) @@ -204,10 +205,12 @@ EXPORT_SYMBOL(_raw_write_lock_wait_flags); int _raw_write_trylock_retry(arch_rwlock_t *rw) { + unsigned int old; int count = spin_retry; while (count-- > 0) { - if (!arch_write_can_lock(rw)) + old = ACCESS_ONCE(rw->lock); + if (old) continue; if (_raw_compare_and_swap(&rw->lock, 0, 0x80000000)) return 1; |