| Message ID | 1380201996-17445-1-git-send-email-jbacik@fusionio.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
* Josef Bacik <jbacik@fusionio.com> wrote: > 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> Acked-by: Ingo Molnar <mingo@kernel.org> Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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);
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(+)