ping, Ingo?
On Thu, 2013-05-30 at 18:12 -0700, Davidlohr Bueso wrote:
> ping?
>
> On Thu, 2013-05-23 at 16:59 -0700, Davidlohr Bueso wrote:
> > From: Davidlohr Bueso <davidlohr.bu...@hp.com>
> >
> > Upon entering the slowpath, we immediately attempt to acquire the lock
> > by checking if it is already unlocked. If we are lucky enough that this
> > is the case, then we don't need to deal with any waiter related logic.
> >
> > Furthermore any checks for an empty wait_list are unnecessary as we
> > already know that count is non-negative and hence no one is waiting for
> > the lock.
> >
> > Move the count check and xchg calls to be done before any waiters are
> > setup - including waiter debugging. Upon failure to acquire the lock,
> > the xchg sets the counter to 0, instead of -1 as it was originally.
> > This can be done here since we set it back to -1 right at the beginning
> > of the loop so other waiters are woken up when the lock is released.
> >
> > When tested on a 8-socket (80 core) system against a vanilla 3.10-rc1
> > kernel, this patch provides some small performance benefits (+2-6%).
> > While it could be considered in the noise level, the average percentages
> > were stable across multiple runs and no performance regressions were seen.
> > Two big winners, for small amounts of users (10-100), were the short and
> > compute workloads had a +19.36% and +%15.76% in jobs per minute.
> >
> > Signed-off-by: Davidlohr Bueso <davidlohr.bu...@hp.com>
> > ---
> > kernel/mutex.c | 26 ++++++++++++++------------
> > 1 file changed, 14 insertions(+), 12 deletions(-)
> >
> > diff --git a/kernel/mutex.c b/kernel/mutex.c
> > index ad53a66..a8cd741 100644
> > --- a/kernel/mutex.c
> > +++ b/kernel/mutex.c
> > @@ -306,7 +306,7 @@ __mutex_lock_common(struct mutex *lock, long state,
> > unsigned int subclass,
> > owner = ACCESS_ONCE(lock->owner);
> > if (owner && !mutex_spin_on_owner(lock, owner)) {
> > mspin_unlock(MLOCK(lock), &node);
> > - break;
> > + goto slowpath;
> > }
> >
> > if ((atomic_read(&lock->count) == 1) &&
> > @@ -314,8 +314,7 @@ __mutex_lock_common(struct mutex *lock, long state,
> > unsigned int subclass,
> > lock_acquired(&lock->dep_map, ip);
> > mutex_set_owner(lock);
> > mspin_unlock(MLOCK(lock), &node);
> > - preempt_enable();
> > - return 0;
> > + goto done;
> > }
> > mspin_unlock(MLOCK(lock), &node);
> >
> > @@ -326,7 +325,7 @@ __mutex_lock_common(struct mutex *lock, long state,
> > unsigned int subclass,
> > * the owner complete.
> > */
> > if (!owner && (need_resched() || rt_task(task)))
> > - break;
> > + goto slowpath;
> >
> > /*
> > * The cpu_relax() call is a compiler barrier which forces
> > @@ -340,6 +339,14 @@ slowpath:
> > #endif
> > spin_lock_mutex(&lock->wait_lock, flags);
> >
> > + /* once more, can we acquire the lock? */
> > + if (MUTEX_SHOW_NO_WAITER(lock) && (atomic_xchg(&lock->count, 0) == 1)) {
> > + lock_acquired(&lock->dep_map, ip);
> > + mutex_set_owner(lock);
> > + spin_unlock_mutex(&lock->wait_lock, flags);
> > + goto done;
> > + }
> > +
> > debug_mutex_lock_common(lock, &waiter);
> > debug_mutex_add_waiter(lock, &waiter, task_thread_info(task));
> >
> > @@ -347,9 +354,6 @@ slowpath:
> > list_add_tail(&waiter.list, &lock->wait_list);
> > waiter.task = task;
> >
> > - if (MUTEX_SHOW_NO_WAITER(lock) && (atomic_xchg(&lock->count, -1) == 1))
> > - goto done;
> > -
> > lock_contended(&lock->dep_map, ip);
> >
> > for (;;) {
> > @@ -363,7 +367,7 @@ slowpath:
> > * other waiters:
> > */
> > if (MUTEX_SHOW_NO_WAITER(lock) &&
> > - (atomic_xchg(&lock->count, -1) == 1))
> > + (atomic_xchg(&lock->count, -1) == 1))
> > break;
> >
> > /*
> > @@ -388,9 +392,8 @@ slowpath:
> > spin_lock_mutex(&lock->wait_lock, flags);
> > }
> >
> > -done:
> > + /* got the lock - cleanup and rejoice! */
> > lock_acquired(&lock->dep_map, ip);
> > - /* got the lock - rejoice! */
> > mutex_remove_waiter(lock, &waiter, current_thread_info());
> > mutex_set_owner(lock);
> >
> > @@ -399,10 +402,9 @@ done:
> > atomic_set(&lock->count, 0);
> >
> > spin_unlock_mutex(&lock->wait_lock, flags);
> > -
> > debug_mutex_free_waiter(&waiter);
> > +done:
> > preempt_enable();
> > -
> > return 0;
> > }
> >
>
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majord...@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
