RE: [PATCH] vhost: fix unnecessary dirty page logging

["Hu, Jiayu" <jiayu.hu@intel.com>]

> -----Original Message-----
> From: Ding, Xuan <xuan.ding@intel.com>
> Sent: Thursday, July 7, 2022 2:55 PM
> To: maxime.coquelin@redhat.com; Xia, Chenbo <chenbo.xia@intel.com>
> Cc: dev@dpdk.org; Hu, Jiayu <jiayu.hu@intel.com>; He, Xingguang
> <xingguang.he@intel.com>; Yang, YvonneX <yvonnex.yang@intel.com>;
> Jiang, Cheng1 <cheng1.jiang@intel.com>; Ding, Xuan <xuan.ding@intel.com>
> Subject: [PATCH] vhost: fix unnecessary dirty page logging
> 
> 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

Reviewed-by: Jiayu Hu <jiayu.hu@intel.com>

Thanks,
Jiayu