ef6edc9746
On systems running with virtual cpus there is optimization potential in regard to spinlocks and rw-locks. If the virtual cpu that has taken a lock is known to a cpu that wants to acquire the same lock it is beneficial to yield the timeslice of the virtual cpu in favour of the cpu that has the lock (directed yield). With CONFIG_PREEMPT="n" this can be implemented by the architecture without common code changes. Powerpc already does this. With CONFIG_PREEMPT="y" the lock loops are coded with _raw_spin_trylock, _raw_read_trylock and _raw_write_trylock in kernel/spinlock.c. If the lock could not be taken cpu_relax is called. A directed yield is not possible because cpu_relax doesn't know anything about the lock. To be able to yield the lock in favour of the current lock holder variants of cpu_relax for spinlocks and rw-locks are needed. The new _raw_spin_relax, _raw_read_relax and _raw_write_relax primitives differ from cpu_relax insofar that they have an argument: a pointer to the lock structure. Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Paul Mackerras <paulus@samba.org> Cc: Haavard Skinnemoen <hskinnemoen@atmel.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
251 lines
5.2 KiB
C
251 lines
5.2 KiB
C
/* spinlock.h: 64-bit Sparc spinlock support.
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*
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* Copyright (C) 1997 David S. Miller (davem@caip.rutgers.edu)
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*/
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#ifndef __SPARC64_SPINLOCK_H
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#define __SPARC64_SPINLOCK_H
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#include <linux/threads.h> /* For NR_CPUS */
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#ifndef __ASSEMBLY__
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/* To get debugging spinlocks which detect and catch
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* deadlock situations, set CONFIG_DEBUG_SPINLOCK
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* and rebuild your kernel.
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*/
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/* All of these locking primitives are expected to work properly
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* even in an RMO memory model, which currently is what the kernel
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* runs in.
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*
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* There is another issue. Because we play games to save cycles
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* in the non-contention case, we need to be extra careful about
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* branch targets into the "spinning" code. They live in their
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* own section, but the newer V9 branches have a shorter range
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* than the traditional 32-bit sparc branch variants. The rule
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* is that the branches that go into and out of the spinner sections
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* must be pre-V9 branches.
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*/
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#define __raw_spin_is_locked(lp) ((lp)->lock != 0)
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#define __raw_spin_unlock_wait(lp) \
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do { rmb(); \
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} while((lp)->lock)
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static inline void __raw_spin_lock(raw_spinlock_t *lock)
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{
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unsigned long tmp;
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__asm__ __volatile__(
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"1: ldstub [%1], %0\n"
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" membar #StoreLoad | #StoreStore\n"
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" brnz,pn %0, 2f\n"
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" nop\n"
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" .subsection 2\n"
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"2: ldub [%1], %0\n"
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" membar #LoadLoad\n"
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" brnz,pt %0, 2b\n"
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" nop\n"
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" ba,a,pt %%xcc, 1b\n"
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" .previous"
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: "=&r" (tmp)
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: "r" (lock)
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: "memory");
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}
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static inline int __raw_spin_trylock(raw_spinlock_t *lock)
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{
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unsigned long result;
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__asm__ __volatile__(
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" ldstub [%1], %0\n"
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" membar #StoreLoad | #StoreStore"
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: "=r" (result)
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: "r" (lock)
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: "memory");
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return (result == 0UL);
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}
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static inline void __raw_spin_unlock(raw_spinlock_t *lock)
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{
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__asm__ __volatile__(
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" membar #StoreStore | #LoadStore\n"
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" stb %%g0, [%0]"
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: /* No outputs */
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: "r" (lock)
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: "memory");
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}
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static inline void __raw_spin_lock_flags(raw_spinlock_t *lock, unsigned long flags)
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{
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unsigned long tmp1, tmp2;
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__asm__ __volatile__(
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"1: ldstub [%2], %0\n"
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" membar #StoreLoad | #StoreStore\n"
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" brnz,pn %0, 2f\n"
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" nop\n"
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" .subsection 2\n"
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"2: rdpr %%pil, %1\n"
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" wrpr %3, %%pil\n"
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"3: ldub [%2], %0\n"
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" membar #LoadLoad\n"
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" brnz,pt %0, 3b\n"
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" nop\n"
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" ba,pt %%xcc, 1b\n"
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" wrpr %1, %%pil\n"
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" .previous"
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: "=&r" (tmp1), "=&r" (tmp2)
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: "r"(lock), "r"(flags)
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: "memory");
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}
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/* Multi-reader locks, these are much saner than the 32-bit Sparc ones... */
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static void inline __read_lock(raw_rwlock_t *lock)
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{
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unsigned long tmp1, tmp2;
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__asm__ __volatile__ (
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"1: ldsw [%2], %0\n"
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" brlz,pn %0, 2f\n"
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"4: add %0, 1, %1\n"
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" cas [%2], %0, %1\n"
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" cmp %0, %1\n"
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" membar #StoreLoad | #StoreStore\n"
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" bne,pn %%icc, 1b\n"
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" nop\n"
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" .subsection 2\n"
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"2: ldsw [%2], %0\n"
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" membar #LoadLoad\n"
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" brlz,pt %0, 2b\n"
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" nop\n"
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" ba,a,pt %%xcc, 4b\n"
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" .previous"
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: "=&r" (tmp1), "=&r" (tmp2)
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: "r" (lock)
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: "memory");
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}
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static int inline __read_trylock(raw_rwlock_t *lock)
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{
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int tmp1, tmp2;
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__asm__ __volatile__ (
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"1: ldsw [%2], %0\n"
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" brlz,a,pn %0, 2f\n"
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" mov 0, %0\n"
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" add %0, 1, %1\n"
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" cas [%2], %0, %1\n"
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" cmp %0, %1\n"
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" membar #StoreLoad | #StoreStore\n"
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" bne,pn %%icc, 1b\n"
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" mov 1, %0\n"
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"2:"
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: "=&r" (tmp1), "=&r" (tmp2)
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: "r" (lock)
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: "memory");
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return tmp1;
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}
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static void inline __read_unlock(raw_rwlock_t *lock)
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{
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unsigned long tmp1, tmp2;
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__asm__ __volatile__(
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" membar #StoreLoad | #LoadLoad\n"
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"1: lduw [%2], %0\n"
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" sub %0, 1, %1\n"
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" cas [%2], %0, %1\n"
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" cmp %0, %1\n"
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" bne,pn %%xcc, 1b\n"
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" nop"
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: "=&r" (tmp1), "=&r" (tmp2)
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: "r" (lock)
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: "memory");
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}
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static void inline __write_lock(raw_rwlock_t *lock)
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{
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unsigned long mask, tmp1, tmp2;
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mask = 0x80000000UL;
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__asm__ __volatile__(
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"1: lduw [%2], %0\n"
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" brnz,pn %0, 2f\n"
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"4: or %0, %3, %1\n"
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" cas [%2], %0, %1\n"
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" cmp %0, %1\n"
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" membar #StoreLoad | #StoreStore\n"
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" bne,pn %%icc, 1b\n"
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" nop\n"
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" .subsection 2\n"
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"2: lduw [%2], %0\n"
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" membar #LoadLoad\n"
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" brnz,pt %0, 2b\n"
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" nop\n"
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" ba,a,pt %%xcc, 4b\n"
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" .previous"
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: "=&r" (tmp1), "=&r" (tmp2)
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: "r" (lock), "r" (mask)
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: "memory");
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}
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static void inline __write_unlock(raw_rwlock_t *lock)
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{
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__asm__ __volatile__(
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" membar #LoadStore | #StoreStore\n"
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" stw %%g0, [%0]"
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: /* no outputs */
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: "r" (lock)
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: "memory");
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}
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static int inline __write_trylock(raw_rwlock_t *lock)
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{
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unsigned long mask, tmp1, tmp2, result;
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mask = 0x80000000UL;
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__asm__ __volatile__(
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" mov 0, %2\n"
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"1: lduw [%3], %0\n"
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" brnz,pn %0, 2f\n"
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" or %0, %4, %1\n"
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" cas [%3], %0, %1\n"
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" cmp %0, %1\n"
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" membar #StoreLoad | #StoreStore\n"
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" bne,pn %%icc, 1b\n"
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" nop\n"
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" mov 1, %2\n"
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"2:"
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: "=&r" (tmp1), "=&r" (tmp2), "=&r" (result)
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: "r" (lock), "r" (mask)
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: "memory");
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return result;
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}
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#define __raw_read_lock(p) __read_lock(p)
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#define __raw_read_trylock(p) __read_trylock(p)
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#define __raw_read_unlock(p) __read_unlock(p)
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#define __raw_write_lock(p) __write_lock(p)
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#define __raw_write_unlock(p) __write_unlock(p)
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#define __raw_write_trylock(p) __write_trylock(p)
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#define __raw_read_can_lock(rw) (!((rw)->lock & 0x80000000UL))
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#define __raw_write_can_lock(rw) (!(rw)->lock)
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#define _raw_spin_relax(lock) cpu_relax()
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#define _raw_read_relax(lock) cpu_relax()
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#define _raw_write_relax(lock) cpu_relax()
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#endif /* !(__ASSEMBLY__) */
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#endif /* !(__SPARC64_SPINLOCK_H) */
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