[PATCH V3 07/15] vhost_net: calculate last used length once for mergeable buffer

From: Jason Wang <jasowang@redhat.com>
To: mst@redhat.com, jasowang@redhat.com
Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	jfreimann@redhat.com, tiwei.bie@intel.com,
	maxime.coquelin@redhat.com
Subject: [PATCH V3 07/15] vhost_net: calculate last used length once for mergeable buffer
Date: Wed, 17 Jul 2019 06:52:47 -0400	[thread overview]
Message-ID: <20190717105255.63488-8-jasowang@redhat.com> (raw)
In-Reply-To: <20190717105255.63488-1-jasowang@redhat.com>

This patch tries to calculate last used length once instead of
twice. This can help to convert to use shadow used ring API for
RX.

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 drivers/vhost/net.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index cf47e6e348f4..1a67f889cbc1 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -1065,12 +1065,12 @@ static int get_rx_bufs(struct vhost_virtqueue *vq,
 		}
 		heads[headcount].id = cpu_to_vhost32(vq, d);
 		len = iov_length(vq->iov + seg, in);
-		heads[headcount].len = cpu_to_vhost32(vq, len);
 		datalen -= len;
+		heads[headcount].len = cpu_to_vhost32(vq,
+				       datalen >= 0 ? len : len + datalen);
 		++headcount;
 		seg += in;
 	}
-	heads[headcount - 1].len = cpu_to_vhost32(vq, len + datalen);
 	*iovcount = seg;
 	if (unlikely(log))
 		*log_num = nlogs;
-- 
2.18.1

