openvswitch: Optimize sample action for the clone use cases

With the introduction of open flow 'clone' action, the OVS user space can now translate the 'clone' action into kernel datapath 'sample' action, with 100% probability, to ensure that the clone semantics, which is that the packet seen by the clone action is the same as the packet seen by the action after clone, is faithfully carried out in the datapath. While the sample action in the datpath has the matching semantics, its implementation is only optimized for its original use. Specifically, there are two limitation: First, there is a 3 level of nesting restriction, enforced at the flow downloading time. This limit turns out to be too restrictive for the 'clone' use case. Second, the implementation avoid recursive call only if the sample action list has a single userspace action. The main optimization implemented in this series removes the static nesting limit check, instead, implement the run time recursion limit check, and recursion avoidance similar to that of the 'recirc' action. This optimization solve both #1 and #2 issues above. One related optimization attempts to avoid copying flow key as long as the actions enclosed does not change the flow key. The detection is performed only once at the flow downloading time. Another related optimization is to rewrite the action list at flow downloading time in order to save the fast path from parsing the sample action list in its original form repeatedly.

AZandy zhou committed 9 years ago