ofproto: RCU postpone rule destruction.

This allows rules to be used without taking references while RCU
protected.

The last step of destroying an ofproto also needs to be postponed, as
the rule destruction requires the class structure to be available at
the postponed destruction callback.

Signed-off-by: Jarno Rajahalme <jrajahalme@nicira.com>
Acked-by: Ethan Jackson <ethan@nicira.com>
ofproto: Make taking rule reference conditional on lookup.

Prior to this paths the rule lookup functions have always taken a
reference on the found rule before returning.  Make this conditional,
so that unnecessary refs/unrefs can be avoided in a later patch.

Signed-off-by: Jarno Rajahalme <jrajahalme@nicira.com>
Acked-by: Ethan Jackson <ethan@nicira.com>
ofproto: Reduce taking rule references.

Only take reference to a looked up rule when needed.

This reduces the total CPU utilization of rule_ref/unref calls by 80%,
from 5% of total server CPU capacity to 1% in a netperf TCP_CRR
test stressing the userspace.

Signed-off-by: Jarno Rajahalme <jrajahalme@nicira.com>
Acked-by: Ethan Jackson <ethan@nicira.com>