[PATCH] vhost: fix unnecessary dirty page logging

[xuan.ding@intel.com]

From: Xuan Ding <xuan.ding@intel.com>

The dirty page logging is only required in vhost enqueue direction for
live migration. This patch removes the unnecessary dirty page logging
in vhost dequeue direction. Otherwise, it will result in a performance
drop. Some if-else judgements are also optimized to improve performance.

Fixes: 6d823bb302c7 ("vhost: prepare sync for descriptor to mbuf refactoring")
Fixes: b6eee3e83402 ("vhost: fix sync dequeue offload")

Signed-off-by: Xuan Ding <xuan.ding@intel.com>
---
 lib/vhost/virtio_net.c | 31 +++++++++++++------------------
 1 file changed, 13 insertions(+), 18 deletions(-)

diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
index e842c35fef..12b7fbe7f9 100644
--- a/lib/vhost/virtio_net.c
+++ b/lib/vhost/virtio_net.c
@@ -1113,27 +1113,27 @@ sync_fill_seg(struct virtio_net *dev, struct vhost_virtqueue *vq,
 			rte_memcpy((void *)((uintptr_t)(buf_addr)),
 				rte_pktmbuf_mtod_offset(m, void *, mbuf_offset),
 				cpy_len);
+			vhost_log_cache_write_iova(dev, vq, buf_iova, cpy_len);
+			PRINT_PACKET(dev, (uintptr_t)(buf_addr), cpy_len, 0);
 		} else {
 			rte_memcpy(rte_pktmbuf_mtod_offset(m, void *, mbuf_offset),
 				(void *)((uintptr_t)(buf_addr)),
 				cpy_len);
 		}
-		vhost_log_cache_write_iova(dev, vq, buf_iova, cpy_len);
-		PRINT_PACKET(dev, (uintptr_t)(buf_addr), cpy_len, 0);
 	} else {
 		if (to_desc) {
 			batch_copy[vq->batch_copy_nb_elems].dst =
 				(void *)((uintptr_t)(buf_addr));
 			batch_copy[vq->batch_copy_nb_elems].src =
 				rte_pktmbuf_mtod_offset(m, void *, mbuf_offset);
+			batch_copy[vq->batch_copy_nb_elems].log_addr = buf_iova;
+			batch_copy[vq->batch_copy_nb_elems].len = cpy_len;
 		} else {
 			batch_copy[vq->batch_copy_nb_elems].dst =
 				rte_pktmbuf_mtod_offset(m, void *, mbuf_offset);
 			batch_copy[vq->batch_copy_nb_elems].src =
 				(void *)((uintptr_t)(buf_addr));
 		}
-		batch_copy[vq->batch_copy_nb_elems].log_addr = buf_iova;
-		batch_copy[vq->batch_copy_nb_elems].len = cpy_len;
 		vq->batch_copy_nb_elems++;
 	}
 }
@@ -2739,18 +2739,14 @@ desc_to_mbuf(struct virtio_net *dev, struct vhost_virtqueue *vq,
 			if (async_fill_seg(dev, vq, cur, mbuf_offset,
 					   buf_iova + buf_offset, cpy_len, false) < 0)
 				goto error;
+		} else if (likely(hdr && cur == m)) {
+			rte_memcpy(rte_pktmbuf_mtod_offset(cur, void *, mbuf_offset),
+				(void *)((uintptr_t)(buf_addr + buf_offset)),
+				cpy_len);
 		} else {
-			if (hdr && cur == m) {
-				rte_memcpy(rte_pktmbuf_mtod_offset(cur, void *, mbuf_offset),
-					(void *)((uintptr_t)(buf_addr + buf_offset)),
-					cpy_len);
-				vhost_log_cache_write_iova(dev, vq, buf_iova + buf_offset, cpy_len);
-				PRINT_PACKET(dev, (uintptr_t)(buf_addr + buf_offset), cpy_len, 0);
-			} else {
-				sync_fill_seg(dev, vq, cur, mbuf_offset,
-					buf_addr + buf_offset,
-					buf_iova + buf_offset, cpy_len, false);
-			}
+			sync_fill_seg(dev, vq, cur, mbuf_offset,
+				      buf_addr + buf_offset,
+				      buf_iova + buf_offset, cpy_len, false);
 		}
 
 		mbuf_avail  -= cpy_len;
@@ -2804,9 +2800,8 @@ desc_to_mbuf(struct virtio_net *dev, struct vhost_virtqueue *vq,
 		async_iter_finalize(async);
 		if (hdr)
 			pkts_info[slot_idx].nethdr = *hdr;
-	} else {
-		if (hdr)
-			vhost_dequeue_offload(dev, hdr, m, legacy_ol_flags);
+	} else if (hdr) {
+		vhost_dequeue_offload(dev, hdr, m, legacy_ol_flags);
 	}
 
 	return 0;
-- 
2.17.1