Messages in this thread | | | Date | Tue, 13 Oct 2015 21:56:27 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v7 4/5] locking/pvqspinlock: Allow 1 lock stealing attempt |
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On Tue, Sep 22, 2015 at 04:50:43PM -0400, Waiman Long wrote:
> +gotlock: > /* > + * We now have the lock. We need to either clear the tail code or > + * notify the next one in queue as the new queue head. > */ > + old = atomic_read(&lock->val); > + while ((old & _Q_TAIL_MASK) == tail) { > + int val; > + int new = old & ~_Q_TAIL_MASK; > + > + /* > + * We are the only one in the queue, so clear the tail code > + * and return. > + */ > + val = atomic_cmpxchg(&lock->val, old, new); > + if (old == val) > + goto done; > + old = val; > + } > +
This i need to think about a wee bit; its almost the same...
So the below is exactly duplicated from the normal slowpath, so why don't you keep that there?
It would get you something like:
if (pv_wait_head_or_steal(..)) goto stolen;
stolen: > + /* > + * contended path; wait for next, release. > + */ > + while (!(next = READ_ONCE(node->next))) > + cpu_relax(); > + > + arch_mcs_spin_unlock_contended(&next->locked); > + pv_kick_node(lock, next);
release: ...
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