* Sasha Levin (levinsasha928@gmail.com) wrote:

Hi Mathieu,

On Mon, Oct 29, 2012 at 9:29 AM, Mathieu Desnoyers
[off-list ref] wrote:

quoted

* Sasha Levin (levinsasha928@gmail.com) wrote:
[...]

quoted

-static struct hlist_head *hash_bucket(struct net *net, const char *name)
-{
-     unsigned int hash = jhash(name, strlen(name), (unsigned long) net);
-     return &dev_table[hash & (VPORT_HASH_BUCKETS - 1)];
-}
-
 /**
  *   ovs_vport_locate - find a port that has already been created
  *

@@ -84,13 +76,12 @@ static struct hlist_head *hash_bucket(struct net *net, const char *name)
  */
 struct vport *ovs_vport_locate(struct net *net, const char *name)
 {
-     struct hlist_head *bucket = hash_bucket(net, name);
      struct vport *vport;
      struct hlist_node *node;
+     int key = full_name_hash(name, strlen(name));

-     hlist_for_each_entry_rcu(vport, node, bucket, hash_node)
-             if (!strcmp(name, vport->ops->get_name(vport)) &&
-                 net_eq(ovs_dp_get_net(vport->dp), net))
+     hash_for_each_possible_rcu(dev_table, vport, node, hash_node, key)

Is applying hash_32() on top of full_name_hash() needed and expected ?

Since this was pointed out in several of the patches, I'll answer it
just once here.

I've intentionally "allowed" double hashing with hash_32 to keep the
code simple.

hash_32() is pretty simple and gcc optimizes it to be almost nothing,
so doing that costs us a multiplication and a shift. On the other
hand, we benefit from keeping our code simple - how would we avoid
doing this double hash? adding a different hashtable function for
strings? or a new function for already hashed keys? I think we benefit
a lot from having to mul/shr instead of adding extra lines of code
here.

This could be done, as I pointed out in another email within this
thread, by changing the "key" argument from add/for_each_possible to an
expected "hash" value, and let the caller invoke hash_32() if they want.
I doubt this would add a significant amount of complexity for users of
this API, but would allow much more flexibility to choose hash
functions.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>