On Sun, Mar 25, 2007 at 07:54:07PM +0400, Oleg Nesterov wrote:
> I am sorry for being completely off-topic, but I've been wondering for the
> long time...
>
> What if we replace raw_spinlock_t.slock with "struct task_struct *owner" ?
>
> void _spin_lock(spinlock_t *lock)
> {
> struct task_struct *owner;
>
> for (;;) {
> preempt_disable();
> if (likely(_raw_spin_trylock(lock)))
> break;
> preempt_enable();
>
> while (!spin_can_lock(lock)) {
> rcu_read_lock();
> owner = lock->owner;
> if (owner && current->prio < owner->prio &&
> !test_tsk_thread_flag(owner,
> TIF_NEED_RESCHED))
> set_tsk_thread_flag(owner,
> TIF_NEED_RESCHED);
> rcu_read_unlock();
> cpu_relax();
> }
> }
>
> lock->owner = current;
> }
>
> void _spin_unlock(spinlock_t *lock)
> {
> lock->owner = NULL;
> _raw_spin_unlock(lock);
> preempt_enable();
> }
>
> Now we don't need need_lockbreak(lock), need_resched() is enough, and we take
> ->prio into consideration.
>
> Makes sense? Or stupid?
Well with my queued spinlocks, all that lockbreak stuff can just come out
of the spin_lock, break_lock out of the spinlock structure, and
need_lockbreak just becomes (lock->qhead - lock->qtail > 1).
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