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.

Signed-off-by: Andy Zhou <azhou@ovn.org>
Acked-by: Pravin B Shelar <pshelar@ovn.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 15 insertions, 0 deletions

diff --git a/include/uapi/linux/openvswitch.h b/include/uapi/linux/openvswitch.h
index 7f41f7d0000f..66d1c3ccfd8e 100644
--- a/include/uapi/linux/openvswitch.h
+++ b/include/uapi/linux/openvswitch.h
@@ -578,10 +578,25 @@ enum ovs_sample_attr {
 	OVS_SAMPLE_ATTR_PROBABILITY, /* u32 number */
 	OVS_SAMPLE_ATTR_ACTIONS,     /* Nested OVS_ACTION_ATTR_* attributes. */
 	__OVS_SAMPLE_ATTR_MAX,
+
+#ifdef __KERNEL__
+	OVS_SAMPLE_ATTR_ARG          /* struct sample_arg  */
+#endif
 };
 
 #define OVS_SAMPLE_ATTR_MAX (__OVS_SAMPLE_ATTR_MAX - 1)
 
+#ifdef __KERNEL__
+struct sample_arg {
+	bool exec;                   /* When true, actions in sample will not
+				      * change flow keys. False otherwise.
+				      */
+	u32  probability;            /* Same value as
+				      * 'OVS_SAMPLE_ATTR_PROBABILITY'.
+				      */
+};
+#endif
+
 /**
  * enum ovs_userspace_attr - Attributes for %OVS_ACTION_ATTR_USERSPACE action.
  * @OVS_USERSPACE_ATTR_PID: u32 Netlink PID to which the %OVS_PACKET_CMD_ACTION