Re: [PATCH-queue/locking/core] locking/mutex: Unify yield_to_waiter & waiter_spinning

[Waiman Long]

On 08/18/2016 09:28 PM, Jason Low wrote:
> On Thu, 2016-08-18 at 21:15 -0400, Waiman Long wrote:
> > Both waiter_spinning and yield_to_waiter are used for somewhat similar
> > purpose. The waiter_spinning flag is used in CONFIG_MUTEX_SPIN_ON_OWNER
> > to make optimistic spinner yield to spinning waiter; whereas the
> > yield_to_waiter is used in !CONFIG_MUTEX_SPIN_ON_OWNER to make new
> > incoming mutex locker to yield to the sleeping waiter.
> >
> > This patch unifies these 2 flags into a single yield_to_waiter
> > flag that is used in both CONFIG_MUTEX_SPIN_ON_OWNER and
> > !CONFIG_MUTEX_SPIN_ON_OWNER codes.
> >
> > Signed-off-by: Waiman Long<Waiman.Long@xxxxxxx>
> > ---
> >   include/linux/mutex.h  |    8 ++++++--
> >   kernel/locking/mutex.c |   12 ++++++------
> >   2 files changed, 12 insertions(+), 8 deletions(-)
> >
> > diff --git a/include/linux/mutex.h b/include/linux/mutex.h
> > index 988c020..2b3dcdb 100644
> > --- a/include/linux/mutex.h
> > +++ b/include/linux/mutex.h
> > @@ -57,8 +57,12 @@ struct mutex {
> >   #endif
> >   #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
> >   	struct optimistic_spin_queue osq; /* Spinner MCS lock */
> > -	int waiter_spinning;
> > -#elif defined(CONFIG_SMP)
> > +#endif
> > +#ifdef CONFIG_SMP
> > +	/*
> > +	 * Used by both CONFIG_MUTEX_SPIN_ON_OWNER (depends on CONFIG_SMP)&
> > +	 * !CONFIG_MUTEX_SPIN_ON_OWNER codes.
> > +	 */
> >   	int yield_to_waiter;
> >   #endif
> >   #ifdef CONFIG_DEBUG_MUTEXES
> > diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
> > index c4261fa..7218835 100644
> > --- a/kernel/locking/mutex.c
> > +++ b/kernel/locking/mutex.c
> > @@ -55,8 +55,8 @@ __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
> >   	mutex_clear_owner(lock);
> >   #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
> >   	osq_lock_init(&lock->osq);
> > -	lock->waiter_spinning = false;
> > -#elif defined(CONFIG_SMP)
> > +#endif
> > +#ifdef CONFIG_SMP
> >   	lock->yield_to_waiter = false;
> >   #endif
> >
> > @@ -351,7 +351,7 @@ static bool mutex_optimistic_spin(struct mutex *lock,
> >   		 * Turn on the waiter spinning flag to discourage the spinner
> >   		 * from getting the lock.
> Might want to update this comment to "Turn on the yield to waiter flag
> to discourage optimistic spinners from stealing the lock."
>
> Besides that:
>
> Acked-by: Jason Low<jason.low2@xxxxxxx>

You are right. I should have made that comment change. As you have a new 
patch outstanding, I will wait a bit until it stabilizes before I update 
my patch.

Cheers,
Longman