On Fri, Sep 19, 2014 at 03:05:27PM +0100, Thomas Graf wrote:
> On 09/18/14 at 10:55am, Simon Horman wrote:
> > +const struct nlattr *bucket_actions(const struct nlattr *attr)
> > +{
> > + const struct nlattr *a;
> > + int rem;
> > +
> > + for (a = nla_data(attr), rem = nla_len(attr); rem > 0;
> > + a = nla_next(a, &rem)) {
> > + if (nla_type(a) == OVS_BUCKET_ATTR_ACTIONS) {
> > + return a;
> > + }
> > + }
> > +
> > + return NULL;
> > +}
>
> This is identical to nla_find(). I realize this is not the only
> example but I think we should stop replicating existing Netlink
> functionality and add missing pieces to lib/nlattr.c.
Thanks. For starters I have removed bucket_actions() and replaced
its usage with a call to nla_find().
> > +static u16 bucket_weight(const struct nlattr *attr)
> > +{
> > + const struct nlattr *weight;
> > +
> > + /* validate_and_copy_bucket() ensures that the first
> > + * attribute is OVS_BUCKET_ATTR_WEIGHT */
> > + weight = nla_data(attr);
> > + BUG_ON(nla_type(weight) != OVS_BUCKET_ATTR_WEIGHT);
> > + return nla_get_u16(weight);
> > +}
> > +
> > +static int select_group(struct datapath *dp, struct sk_buff *skb,
> > + const struct nlattr *attr)
> > +{
> > + const struct nlattr *best_bucket = NULL;
> > + const struct nlattr *acts_list;
> > + const struct nlattr *bucket;
> > + struct sk_buff *sample_skb;
> > + u32 best_score = 0;
> > + u32 basis;
> > + u32 i = 0;
> > + int rem;
> > +
> > + basis = skb_get_hash(skb);
> > +
> > + /* Only possible type of attributes is OVS_SELECT_GROUP_ATTR_BUCKET */
> > + for (bucket = nla_data(attr), rem = nla_len(attr); rem > 0;
> > + bucket = nla_next(bucket, &rem)) {
> > + uint16_t weight = bucket_weight(bucket);
>
> I think we should validate only once when we copy then assume it is
> correct.
That is the intention of this code, is it doing something else?
I think there is some scope to store the bucket in a more efficient
form for execution. But I'm not sure that any other actions
receive such treatment. So I postponed inventing that wheel.
> > + // XXX: This hashing seems expensive
> > + u32 score = (jhash_1word(i, basis) & 0xffff) * weight;
>
> Maybe just calculate a weighted distribution table pointing to the
> buckets which you index with 8 bits of the hash.
Nice idea. I think that would work out quite well.
The main question for me would be where to store such a table,
which comes back to my remark above about more storing a more
efficient efficient form of the action.
> > + if (score >= best_score) {
> > + best_bucket = bucket;
> > + best_score = score;
> > + }
> > + i++;
> > + }
> > +
> > + acts_list = bucket_actions(best_bucket);
> > +
> > + /* A select group action is always the final action so
> > + * there is no need to clone the skb in case of side effects.
> > + * Instead just take a reference to it which will be released
> > + * by do_execute_actions(). */
> > + skb_get(skb);
> > +
> > + return do_execute_actions(dp, skb, nla_data(acts_list),
> > + nla_len(acts_list));
>
> Do we need a recursion limit here?
I believe that is already handled by the depth check that occurs
when the actions are copied.
_______________________________________________
dev mailing list
dev@openvswitch.org
http://openvswitch.org/mailman/listinfo/dev
