On Fri, May 30, 2014 at 11:43:52AM -0400, Waiman Long wrote: > --- > kernel/locking/qspinlock.c | 18 ++++++++++++++++-- > 1 files changed, 16 insertions(+), 2 deletions(-) > > diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c > index fc7fd8c..7f10758 100644 > --- a/kernel/locking/qspinlock.c > +++ b/kernel/locking/qspinlock.c > @@ -233,11 +233,25 @@ void queue_spin_lock_slowpath(struct qspinlock *lock, u32 val) > */ > for (;;) { > /* > - * If we observe any contention; queue. > + * If we observe that the queue is not empty or both > + * the pending and lock bits are set, queue > */ > - if (val & ~_Q_LOCKED_MASK) > + if ((val & _Q_TAIL_MASK) || > + (val == (_Q_LOCKED_VAL|_Q_PENDING_VAL))) > goto queue; > > + if (val == _Q_PENDING_VAL) { > + /* > + * Pending bit is set, but not the lock bit. > + * Assuming that the pending bit holder is going to > + * set the lock bit and clear the pending bit soon, > + * it is better to wait than to exit at this point. > + */ > + cpu_relax(); > + val = atomic_read(&lock->val); > + continue; > + } > + > new = _Q_LOCKED_VAL; > if (val == new) > new |= _Q_PENDING_VAL; So, again, you just posted a new version without replying to the previous discussion; so let me try again, what's wrong with the proposal here: lkml.kernel.org/r/20140417163640.GT11096@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
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