Add Macro for Running Flow Table Lookup (#147)

Running a flow table lookup on every packet is expensive and as the
functionality isn't always used we have decided to create a macro to
disable it. The functionality will still be enabled by default, but if
it is unused disabling it should boost performance. 

Commit log:

* Macros for running flow table lookup

* Updated comment about disabling flow table lookup

onvm/onvm_mgr/Makefile

@@ -35,6 +35,9 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+# set this to 0 to disable flow table lookup for incoming packets
+ENABLE_FLOW_LOOKUP=1
+
 ifeq ($(RTE_SDK),)
 $(error "Please define RTE_SDK environment variable")
 endif
@@ -62,6 +65,10 @@ CFLAGS += -I$(SRCDIR)/../ -I$(SRCDIR)/../onvm_nflib/ -I$(SRCDIR)/../lib/
 LDFLAGS += $(SRCDIR)/../lib/$(RTE_TARGET)/libonvmhelper.a
 LDFLAGS += $(SRCDIR)/../onvm_nflib/$(RTE_TARGET)/libonvm.a
 
+ifeq ($(ENABLE_FLOW_LOOKUP), 1)
+CFLAGS +=-D FLOW_LOOKUP
+endif
+
 # for newer gcc, e.g. 4.4, no-strict-aliasing may not be necessary
 # and so the next line can be removed in those cases.
 EXTRA_CFLAGS += -fno-strict-aliasing

onvm/onvm_mgr/onvm_pkt.c

@@ -57,9 +57,11 @@ void
 onvm_pkt_process_rx_batch(struct queue_mgr *rx_mgr, struct rte_mbuf *pkts[], uint16_t rx_count) {
         uint16_t i;
         struct onvm_pkt_meta *meta;
+#ifdef FLOW_LOOKUP
         struct onvm_flow_entry *flow_entry;
         struct onvm_service_chain *sc;
         int ret;
+#endif
 
         if (rx_mgr == NULL || pkts == NULL)
                 return;
@@ -68,15 +70,19 @@ onvm_pkt_process_rx_batch(struct queue_mgr *rx_mgr, struct rte_mbuf *pkts[], uin
                 meta = (struct onvm_pkt_meta *)&(((struct rte_mbuf *)pkts[i])->udata64);
                 meta->src = 0;
                 meta->chain_index = 0;
+#ifdef FLOW_LOOKUP
                 ret = onvm_flow_dir_get_pkt(pkts[i], &flow_entry);
                 if (ret >= 0) {
                         sc = flow_entry->sc;
                         meta->action = onvm_sc_next_action(sc, pkts[i]);
                         meta->destination = onvm_sc_next_destination(sc, pkts[i]);
                 } else {
+#endif
                         meta->action = onvm_sc_next_action(default_chain, pkts[i]);
                         meta->destination = onvm_sc_next_destination(default_chain, pkts[i]);
+#ifdef FLOW_LOOKUP
                 }
+#endif
                 /* PERF: this might hurt performance since it will cause cache
                  * invalidations. Ideally the data modified by the NF manager
                  * would be a different line than that modified/read by NFs.