On Thu, 05 Oct 2017, Waiman Long wrote:
Insertion and deletion is relatively cheap and mostly contention
free for dlock-list. Lookup, on the other hand, can be rather costly
because all the lists in a dlock-list will have to be iterated.
Currently dlock-list insertion is based on the cpu that the task is
running on. So a given object can be inserted into any one of the
lists depending on what the current cpu is.
This patch provides an alternative way of list selection. The caller
can provide a object context which will be hashed to one of the list
in a dlock-list. The object can then be added into that particular
list. Lookup can be done by iterating elements in the provided list
only instead of all the lists in a dlock-list.
Unless I'm misusing the api, I could not find a standard way of
iterating a _particular_ list head (the one the dlock_list_hash()
returned). This is because iterators always want the all the heads.
Also, in my particular epoll case I'd need the head->lock _not_ to
be dropped after the iteration, and therefore is pretty adhoc.
Currently we do:
dlist_for_each_entry() {
// acquire head->lock for each list
}
// no locks held
dlist_add()
I'm thinking perhaps we could have dlist_check_add() which passes a
callback to ensure we want to add the node. The function could acquire
the head->lock and not release it until the very end.
Thanks,
Davidlohr
