| Message ID | 1379605688-987-1-git-send-email-jbacik@fusionio.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 09/19/2013 11:48 AM, Josef Bacik 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> > --- > 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 | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h > index 0616ffe..c340493 100644 > --- a/include/linux/rwsem.h > +++ b/include/linux/rwsem.h > @@ -75,6 +75,19 @@ 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 the opposite type is wanting access to the ^^^^^^^^^^^^^ Readers can infer that at least one writer is waiting if the wait_list is !empty; however, writers cannot infer anything other than some other thread is waiting -- it could be a reader or a writer or multiples of either. > + * lock. > + */ > +static inline int rwsem_is_contended(struct rw_semaphore *sem) > +{ > + if (!list_empty(&sem->wait_list)) > + return 1; > + return 0; How about return !list_empty(&sem->wait_list); ? > +} > + > +/* > * lock for reading > */ > extern void down_read(struct rw_semaphore *sem); > -- 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
On Thu, Sep 19, 2013 at 06:57:27PM -0400, Peter Hurley wrote: > On 09/19/2013 11:48 AM, Josef Bacik 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> > >--- > >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 | 13 +++++++++++++ > > 1 file changed, 13 insertions(+) > > > >diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h > >index 0616ffe..c340493 100644 > >--- a/include/linux/rwsem.h > >+++ b/include/linux/rwsem.h > >@@ -75,6 +75,19 @@ 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 the opposite type is wanting access to the > ^^^^^^^^^^^^^ > > Readers can infer that at least one writer is waiting if the wait_list is > !empty; however, writers cannot infer anything other than some other > thread is waiting -- it could be a reader or a writer or multiples of either. > Right duh, I'll fix that up. > > >+ * lock. > >+ */ > >+static inline int rwsem_is_contended(struct rw_semaphore *sem) > >+{ > >+ if (!list_empty(&sem->wait_list)) > >+ return 1; > >+ return 0; > > How about > > return !list_empty(&sem->wait_list); > > ? > Another duh, thanks I'll wait for any other input and then fix this up and resend. Thanks, Josef -- 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..c340493 100644 --- a/include/linux/rwsem.h +++ b/include/linux/rwsem.h @@ -75,6 +75,19 @@ 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 the opposite type is wanting access to the + * lock. + */ +static inline int rwsem_is_contended(struct rw_semaphore *sem) +{ + if (!list_empty(&sem->wait_list)) + return 1; + return 0; +} + +/* * 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> --- 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 | 13 +++++++++++++ 1 file changed, 13 insertions(+)