gk: prefetch the transmission fields of packets

This patch prefetches the transmission fields of a packet when
it is ready to be prepared for transmission.

gk/co.c

@@ -337,6 +337,30 @@ priority_from_delta_time(uint64_t present, uint64_t past)
 	return integer_log_base_2(delta_time);
 }
 
+/* TODO This should be part of DPDK. */
+/**
+ * Prefetch the second part of the mbuf
+ *
+ * The next 64 bytes of the mbuf corresponds to fields that are used in the
+ * transmit path. If the cache line of the architecture is higher than 64B,
+ * this function does nothing as it is expected that the full mbuf is
+ * already in cache.
+ *
+ * @param m
+ *   The pointer to the mbuf.
+ */
+static inline bool
+rte_mbuf_prefetch_part2_non_temporal(struct rte_mbuf *m)
+{
+#if RTE_CACHE_LINE_SIZE == 64
+	rte_prefetch_non_temporal(&m->cacheline1);
+	return true;
+#else
+	RTE_SET_USED(m);
+	return false;
+#endif
+}
+
 /*
  * When a flow entry is at request state, all the GK block processing
  * that entry does is to:
@@ -389,6 +413,10 @@ gk_process_request(struct gk_co *this_co, struct flow_entry *fe,
 
 	/* The assigned priority is @priority. */
 
+	/* Prepare packet for transmission. */
+	if (likely(rte_mbuf_prefetch_part2_non_temporal(pkt)))
+		yield_next(this_co);
+
 	/* Encapsulate the packet as a request. */
 	ret = encapsulate(pkt, priority, back, &fib->u.grantor.gt_addr);
 	if (ret < 0)
@@ -462,6 +490,10 @@ gk_process_granted(struct gk_co *this_co, struct flow_entry *fe,
 		priority = PRIORITY_RENEW_CAP;
 	}
 
+	/* Prepare packet for transmission. */
+	if (likely(rte_mbuf_prefetch_part2_non_temporal(pkt)))
+		yield_next(this_co);
+
 	/*
 	 * Encapsulate packet as a granted packet,
 	 * mark it as a capability renewal request if @renew_cap is true,
@@ -537,6 +569,9 @@ gk_process_bpf(struct gk_co *this_co, struct flow_entry *fe,
 	if (unlikely(now >= fe->u.bpf.expire_at))
 		goto expired;
 
+	/*
+	 * TODO Prepare packet for transmission before encapsulate() is called.
+	 */
 	program_index = fe->program_index;
 	rc = gk_bpf_decide_pkt(gk_conf, program_index, fe, packet, now,
 		&bpf_ret);