Messages in this thread Patch in this message | | | From | Josef Bacik <> | Subject | [PATCH 1/2] rwsem: add rwsem_is_contended V3 | Date | Thu, 26 Sep 2013 09:26:35 -0400 |
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Btrfs needs a simple way to know if it needs to let go of it's read lock on a rwsem. Introduce rwsem_is_contended to check to see if there are any waiters on this rwsem currently. This is just a hueristic, it is meant to be light and not 100% accurate and called by somebody already holding on to the rwsem in either read or write. Thanks,
Signed-off-by: Josef Bacik <jbacik@fusionio.com> --- V2->V3: fixed the comment and simplified the function as per Peter's suggestions.
V1->V2: took everybodys suggestions and simplified it to just one function in rwsem.h so it works for both the spinlock case and non-spinlock case.
include/linux/rwsem.h | 11 +++++++++++ 1 file changed, 11 insertions(+)
diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h index 0616ffe..03f3b05 100644 --- a/include/linux/rwsem.h +++ b/include/linux/rwsem.h @@ -75,6 +75,17 @@ do { \ } while (0) /* + * This is the same regardless of which rwsem implementation that is being used. + * It is just a heuristic meant to be called by somebody alreadying holding the + * rwsem to see if somebody from an incompatible type is wanting access to the + * lock. + */ +static inline int rwsem_is_contended(struct rw_semaphore *sem) +{ + return !list_empty(&sem->wait_list); +} + +/* * lock for reading */ extern void down_read(struct rw_semaphore *sem); -- 1.8.3.1
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