On Wed, Apr 01, 2015 at 02:54:45PM -0400, Waiman Long wrote:
On 04/01/2015 02:17 PM, Peter Zijlstra wrote:oh but the crux is that you guarantee a lookup will find an entry. it will
On Wed, Apr 01, 2015 at 07:42:39PM +0200, Peter Zijlstra wrote:I think it doesn't matter who did the unhashing. Multiple independent locks
The idea being that the result is that any lookup is guaranteed to findHohumm.. time to think more I think ;-)So bear with me, I've not really pondered this well so it could be full
of holes (again).
After the cmpxchg(&l->locked, _Q_LOCKED_VAL, _Q_SLOW_VAL) succeeds the
spin_unlock() must do the hash lookup, right? We can make the lookup
unhash.
If the cmpxchg() fails the unlock will not do the lookup and we must
unhash.
an entry, which reduces our worst case lookup cost to whatever the worst
case insertion cost was.
can be hashed to the same value. Since they can be unhashed independently,
there is no way to know whether you have checked all the possible buckets.
never need to iterate the entire array.