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lib: Provide generic atomic64_t implementation

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Many processor architectures have no 64-bit atomic instructions, but
we need atomic64_t in order to support the perf_counter subsystem.

This adds an implementation of 64-bit atomic operations using hashed
spinlocks to provide atomicity.  For each atomic operation, the address
of the atomic64_t variable is hashed to an index into an array of 16
spinlocks.  That spinlock is taken (with interrupts disabled) around the
operation, which can then be coded non-atomically within the lock.

On UP, all the spinlock manipulation goes away and we simply disable
interrupts around each operation.  In fact gcc eliminates the whole
atomic64_lock variable as well.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Paul Mackerras
2009-06-12 21:10:05 +00:00
committed by Benjamin Herrenschmidt
parent 4c75f84f2c
commit 09d4e0edd4
4 changed files with 225 additions and 0 deletions
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6
lib/Kconfig
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@ -194,4 +194,10 @@ config DISABLE_OBSOLETE_CPUMASK_FUNCTIONS
config NLATTR
bool
#
# Generic 64-bit atomic support is selected if needed
#
config GENERIC_ATOMIC64
bool
endmenu