[PATCH RT] rt: add rwsem_is_contended() definition to rwsem_rt.h

[PATCH RT] rt: add rwsem_is_contended() definition to rwsem_rt.h

[Clark Williams]

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Thomas,

The latest btrfs code uses rwsem_is_contended() in the function
caching_thread(). On RT systems, include/linux/rwsem.h is replaced with
include/linux/rwsem_rt.h which does not provide a definition for
rwsem_is_contended().  This commit provides a definition that should
work on RT (where the lock is actually an rt_mutex).

Signed-off-by: Clark Williams <williams@redhat.com>
---
 include/linux/rwsem_rt.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/linux/rwsem_rt.h b/include/linux/rwsem_rt.h
index e94d945c5844..77035d7abc04 100644
--- a/include/linux/rwsem_rt.h
+++ b/include/linux/rwsem_rt.h
@@ -125,4 +125,9 @@ static inline void down_write_nest_lock(struct rw_semaphore *sem,
        rt_down_write_nested_lock(sem, NULL);
 }
 #endif
+
+static inline int rwsem_is_contended(struct rw_semaphore *sem)
+{
+       return !plist_head_empty(&sem->lock.wait_list);
+}
 #endif

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Re: [PATCH RT] rt: add rwsem_is_contended() definition to rwsem_rt.h

[Sebastian Andrzej Siewior]

* Clark Williams | 2014-08-27 16:09:28 [-0500]:

>Thomas,
>
>The latest btrfs code uses rwsem_is_contended() in the function
>caching_thread(). On RT systems, include/linux/rwsem.h is replaced with
>include/linux/rwsem_rt.h which does not provide a definition for
>rwsem_is_contended().  This commit provides a definition that should
>work on RT (where the lock is actually an rt_mutex).

I see that I added rwsem_is_contended() in v3.14-rt1 which does:
|static inline int rwsem_is_contended(struct rw_semaphore *sem)
|{
|      /* rt_mutex_has_waiters() */
|      return !RB_EMPTY_ROOT(&sem->lock.waiters);
|}

Do you lack this in kernel prior to v3.14?

Sebastian

Re: [PATCH RT] rt: add rwsem_is_contended() definition to rwsem_rt.h

[Clark Williams]

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On Tue, 17 Feb 2015 11:09:11 +0100
Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:

> * Clark Williams | 2014-08-27 16:09:28 [-0500]:
> 
> >Thomas,
> >
> >The latest btrfs code uses rwsem_is_contended() in the function
> >caching_thread(). On RT systems, include/linux/rwsem.h is replaced with
> >include/linux/rwsem_rt.h which does not provide a definition for
> >rwsem_is_contended().  This commit provides a definition that should
> >work on RT (where the lock is actually an rt_mutex).
> 
> I see that I added rwsem_is_contended() in v3.14-rt1 which does:
> |static inline int rwsem_is_contended(struct rw_semaphore *sem)
> |{
> |      /* rt_mutex_has_waiters() */
> |      return !RB_EMPTY_ROOT(&sem->lock.waiters);
> |}
> 
> Do you lack this in kernel prior to v3.14?
> 
> Sebastian

Yes, that was the problem. I was back-porting to a 3.10 and was missing
the definition. Sorry for the noise.

Clark

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