Refactor cache line unlock #855
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Signed-off-by: Michal Mielewczyk <[email protected]>
Signed-off-by: Michal Mielewczyk <[email protected]>
Signed-off-by: Michal Mielewczyk <[email protected]>
In the original loop, if a cache line had multiple waiters, there was
a redundant trylock() after admitting the write lock to the first waiter.
Returning just after write-locking the cache line eliminates the redundant
trylock() and reduces the number of accesses to atomic variables.
The second issue with the original code was caused by sharing waiter lists
between different cache lines. Even if the first waiter was admitted the write
lock, the loop was iterating over the waiter list until:
a) finding another waiter to the same cache line; in this case it tried to
lock the cache line which has just been write-locked so the operation
always failed
b) reaching the end of the waiter list.
In both cases it makes no sense to continue iterating after admitting the write
lock to the first watier.
Signed-off-by: Michal Mielewczyk <[email protected]>
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