From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:54937) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gw33E-0000wZ-KO for qemu-devel@nongnu.org; Tue, 19 Feb 2019 05:55:05 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gw33D-0002SR-OZ for qemu-devel@nongnu.org; Tue, 19 Feb 2019 05:55:00 -0500 Received: from mx1.redhat.com ([209.132.183.28]:57440) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gw33D-0002Rn-Ih for qemu-devel@nongnu.org; Tue, 19 Feb 2019 05:54:59 -0500 Date: Tue, 19 Feb 2019 18:51:55 +0800 From: Wei Xu Message-ID: <20190219105155.GD15343@wei-ubt> References: <1550118402-4057-1-git-send-email-wexu@redhat.com> <1550118402-4057-10-git-send-email-wexu@redhat.com> <1c16f234-af83-23c8-2194-94be63574299@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1c16f234-af83-23c8-2194-94be63574299@redhat.com> Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH v4 09/11] virtio-net: update the head descriptor in a chain lastly List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jason Wang Cc: qemu-devel@nongnu.org, maxime.coquelin@redhat.com, tiwei.bie@intel.com, jfreiman@redhat.com, mst@redhat.com On Tue, Feb 19, 2019 at 03:23:01PM +0800, Jason Wang wrote: >=20 > On 2019/2/14 =E4=B8=8B=E5=8D=8812:26, wexu@redhat.com wrote: > >From: Wei Xu > > > >This is a helper for packed ring. > > > >To support packed ring, the head descriptor in a chain should be updat= ed > >lastly since no 'avail_idx' like in packed ring to explicitly tell the > >driver side that all payload is ready after having done the chain, so > >the head is always visible immediately. > > > >This patch fills the header after done all the other ones. > > > >Signed-off-by: Wei Xu >=20 >=20 > It's really odd to workaround API issue in the implementation of device= . > Please introduce batched used updating helpers instead. Can you elaborate a bit more? I don't get it as well. The exact batch as vhost-net or dpdk pmd is not supported by userspace backend. The change here is to keep the header descriptor updated at last in case of a chaining descriptors and the helper might not help too much. Wei >=20 > Thanks >=20 >=20 > >--- > > hw/net/virtio-net.c | 11 ++++++++++- > > 1 file changed, 10 insertions(+), 1 deletion(-) > > > >diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c > >index 3f319ef..330abea 100644 > >--- a/hw/net/virtio-net.c > >+++ b/hw/net/virtio-net.c > >@@ -1251,6 +1251,8 @@ static ssize_t virtio_net_receive_rcu(NetClientS= tate *nc, const uint8_t *buf, > > struct virtio_net_hdr_mrg_rxbuf mhdr; > > unsigned mhdr_cnt =3D 0; > > size_t offset, i, guest_offset; > >+ VirtQueueElement head; > >+ int head_len =3D 0; > > if (!virtio_net_can_receive(nc)) { > > return -1; > >@@ -1328,7 +1330,13 @@ static ssize_t virtio_net_receive_rcu(NetClient= State *nc, const uint8_t *buf, > > } > > /* signal other side */ > >- virtqueue_fill(q->rx_vq, elem, total, i++); > >+ if (i =3D=3D 0) { > >+ head_len =3D total; > >+ head =3D *elem; > >+ } else { > >+ virtqueue_fill(q->rx_vq, elem, len, i); > >+ } > >+ i++; > > g_free(elem); > > } > >@@ -1339,6 +1347,7 @@ static ssize_t virtio_net_receive_rcu(NetClientS= tate *nc, const uint8_t *buf, > > &mhdr.num_buffers, sizeof mhdr.num_buffers); > > } > >+ virtqueue_fill(q->rx_vq, &head, head_len, 0); > > virtqueue_flush(q->rx_vq, i); > > virtio_notify(vdev, q->rx_vq); >=20