[PATCH v5] virtio: optimize stats counters performance

["Morten Brørup" <mb@smartsharesystems.com>]

Optimized the performance of updating the virtio statistics counters by
reducing the number of branches.

Ordered the packet size comparisons according to the probability with
typical internet traffic mix.

Signed-off-by: Morten Brørup <mb@smartsharesystems.com>
---
v5:
* Do not inline the function. (Stephen)
v4:
* Consider multicast/broadcast packets unlikely.
v3:
* Eliminated a local variable.
* Note: Substituted sizeof(uint32_t)*4 by 32UL, using unsigned long type
  to keep optimal offsetting in generated assembler output.
* Removed unnecessary curly braces.
v2:
* Fixed checkpatch warning about line length.
---
 drivers/net/virtio/virtio_rxtx.c | 39 ++++++++++++--------------------
 drivers/net/virtio/virtio_rxtx.h |  4 ++--
 2 files changed, 16 insertions(+), 27 deletions(-)

diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
index f69b9453a2..b67f063b31 100644
--- a/drivers/net/virtio/virtio_rxtx.c
+++ b/drivers/net/virtio/virtio_rxtx.c
@@ -82,37 +82,26 @@ vq_ring_free_chain(struct virtqueue *vq, uint16_t desc_idx)
 }
 
 void
-virtio_update_packet_stats(struct virtnet_stats *stats, struct rte_mbuf *mbuf)
+virtio_update_packet_stats(struct virtnet_stats *const stats,
+		const struct rte_mbuf *const mbuf)
 {
 	uint32_t s = mbuf->pkt_len;
-	struct rte_ether_addr *ea;
+	const struct rte_ether_addr *const ea =
+			rte_pktmbuf_mtod(mbuf, const struct rte_ether_addr *);
 
 	stats->bytes += s;
 
-	if (s == 64) {
-		stats->size_bins[1]++;
-	} else if (s > 64 && s < 1024) {
-		uint32_t bin;
-
-		/* count zeros, and offset into correct bin */
-		bin = (sizeof(s) * 8) - rte_clz32(s) - 5;
-		stats->size_bins[bin]++;
-	} else {
-		if (s < 64)
-			stats->size_bins[0]++;
-		else if (s < 1519)
-			stats->size_bins[6]++;
-		else
-			stats->size_bins[7]++;
-	}
+	if (s >= 1024)
+		stats->size_bins[6 + (s > 1518)]++;
+	else if (s <= 64)
+		stats->size_bins[s >> 6]++;
+	else
+		stats->size_bins[32UL - rte_clz32(s) - 5]++;
 
-	ea = rte_pktmbuf_mtod(mbuf, struct rte_ether_addr *);
-	if (rte_is_multicast_ether_addr(ea)) {
-		if (rte_is_broadcast_ether_addr(ea))
-			stats->broadcast++;
-		else
-			stats->multicast++;
-	}
+	RTE_BUILD_BUG_ON(offsetof(struct virtnet_stats, broadcast) !=
+			offsetof(struct virtnet_stats, multicast) + sizeof(uint64_t));
+	if (unlikely(rte_is_multicast_ether_addr(ea)))
+		(&stats->multicast)[rte_is_broadcast_ether_addr(ea)]++;
 }
 
 static inline void
diff --git a/drivers/net/virtio/virtio_rxtx.h b/drivers/net/virtio/virtio_rxtx.h
index afc4b74534..68034c914b 100644
--- a/drivers/net/virtio/virtio_rxtx.h
+++ b/drivers/net/virtio/virtio_rxtx.h
@@ -35,7 +35,7 @@ struct virtnet_tx {
 };
 
 int virtio_rxq_vec_setup(struct virtnet_rx *rxvq);
-void virtio_update_packet_stats(struct virtnet_stats *stats,
-				struct rte_mbuf *mbuf);
+void virtio_update_packet_stats(struct virtnet_stats *const stats,
+		const struct rte_mbuf *const mbuf);
 
 #endif /* _VIRTIO_RXTX_H_ */
-- 
2.43.0