Messages in this thread Patch in this message | | | Subject | Re: [PATCH][RFC]: mutex: adaptive spin | From | Peter Zijlstra <> | Date | Wed, 07 Jan 2009 00:16:18 +0100 |
| |
On Tue, 2009-01-06 at 23:43 +0100, Peter Zijlstra wrote:
> @@ -115,6 +117,7 @@ void __sched mutex_unlock(struct mutex * > * The unlocking fastpath is the 0->1 transition from 'locked' > * into 'unlocked' state: > */ > + lock->owner = NULL; > __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath); > } >
> +void mutex_spin_or_schedule(struct mutex_waiter *waiter, long state, unsigned long *flags) > +{ > + struct mutex *lock = waiter->lock; > + struct task_struct *task = waiter->task; > + struct task_struct *owner = lock->owner; > + struct rq *rq; > + > + if (!owner) > + goto do_schedule; > + > + rq = task_rq(owner); > + > + if (rq->curr != owner) { > +do_schedule: > + __set_task_state(task, state); > + spin_unlock_mutex(&lock->wait_lock, *flags); > + schedule(); > + } else { > + spin_unlock_mutex(&lock->wait_lock, *flags); > + for (;;) { > + /* Stop spinning when there's a pending signal. */ > + if (signal_pending_state(state, task)) > + break; > + > + /* Owner changed, bail to revalidate state */ > + if (lock->owner != owner) > + break; > + > + /* Owner stopped running, bail to revalidate state */ > + if (rq->curr != owner) > + break; > + > + cpu_relax(); > + } > + } > + spin_lock_mutex(&lock->wait_lock, *flags); > +}
That's not going to work, we set owner to NULL, which means pending spinners get schedule()ed out instead of racing to acquire.
I suppose the below would fix that... really sleep time now
Index: linux-2.6/kernel/sched.c =================================================================== --- linux-2.6.orig/kernel/sched.c +++ linux-2.6/kernel/sched.c @@ -4626,8 +4626,8 @@ do_schedule: if (signal_pending_state(state, task)) break; - /* Owner changed, bail to revalidate state */ - if (lock->owner != owner) + /* Mutex got unlocked, race to acquire. */ + if (!mutex_is_locked(lock)) break; /* Owner stopped running, bail to revalidate state */
| |