Re: [PATCH net-next 5/5] virtio-net: switch off offloads on demand if possible on XDP set

Jason Wang <jasowang@xxxxxxxxxx> · Wed, 19 Jul 2017 10:39:53 +0800

On 2017年07月19日 04:07, Michael S. Tsirkin wrote:
On Mon, Jul 17, 2017 at 08:44:01PM +0800, Jason Wang wrote:
Current XDP implementation want guest offloads feature to be disabled
s/want/wants/

on qemu cli.
on the device.

This is inconvenient and means guest can't benefit from
offloads if XDP is not used. This patch tries to address this
limitation by disable
disabling

the offloads on demand through control guest
offloads. Guest offloads will be disabled and enabled on demand on XDP
set.

Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
In fact, since we no longer reset when XDP is set,
here device might have offloads enabled, buffers are
used but not consumed, then XDP is set.

This can result in
- packet scattered across multiple buffers
   (handled correctly but need to update the comment)

Ok.

- packet may have VIRTIO_NET_HDR_F_NEEDS_CSUM, in that case
   the spec says "The checksum on the packet is incomplete".
   (probably needs to be handled by calculating the checksum).

That's an option. Maybe it's tricky but I was thinking whether or not we 
can just keep the CHECKSUM_PARTIAL here.



Ideas for follow-up patches:

- skip looking at packet data completely
   won't work if you play with checksums dynamically
   but can be done if disabled on device
- allow ethtools to tweak offloads from userspace as well

Right.

Thanks


---
  drivers/net/virtio_net.c | 70 ++++++++++++++++++++++++++++++++++++++++++++----
  1 file changed, 65 insertions(+), 5 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index e732bd6..d970c2d 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -57,6 +57,11 @@ DECLARE_EWMA(pkt_len, 0, 64)
  
  #define VIRTNET_DRIVER_VERSION "1.0.0"
  
+const unsigned long guest_offloads[] = { VIRTIO_NET_F_GUEST_TSO4,
+					 VIRTIO_NET_F_GUEST_TSO6,
+					 VIRTIO_NET_F_GUEST_ECN,
+					 VIRTIO_NET_F_GUEST_UFO };
+
  struct virtnet_stats {
  	struct u64_stats_sync tx_syncp;
  	struct u64_stats_sync rx_syncp;
@@ -164,10 +169,13 @@ struct virtnet_info {
  	u8 ctrl_promisc;
  	u8 ctrl_allmulti;
  	u16 ctrl_vid;
+	u64 ctrl_offloads;
  
  	/* Ethtool settings */
  	u8 duplex;
  	u32 speed;
+
+	unsigned long guest_offloads;
  };
  
  struct padded_vnet_hdr {
@@ -1889,6 +1897,47 @@ static int virtnet_restore_up(struct virtio_device *vdev)
  	return err;
  }
  
+static int virtnet_set_guest_offloads(struct virtnet_info *vi, u64 offloads)
+{
+	struct scatterlist sg;
+	vi->ctrl_offloads = cpu_to_virtio64(vi->vdev, offloads);
+
+	sg_init_one(&sg, &vi->ctrl_offloads, sizeof(vi->ctrl_offloads));
+
+	if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_GUEST_OFFLOADS,
+				  VIRTIO_NET_CTRL_GUEST_OFFLOADS_SET, &sg)) {
+		dev_warn(&vi->dev->dev, "Fail to set guest offload. \n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int virtnet_clear_guest_offloads(struct virtnet_info *vi)
+{
+	u64 offloads = 0;
+
+	if (!vi->guest_offloads)
+		return 0;
+
+	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_CSUM))
+		offloads = 1ULL << VIRTIO_NET_F_GUEST_CSUM;
+
+	return virtnet_set_guest_offloads(vi, offloads);
+}
+
+static int virtnet_restore_guest_offloads(struct virtnet_info *vi)
+{
+	u64 offloads = vi->guest_offloads;
+
+	if (!vi->guest_offloads)
+		return 0;
+	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_CSUM))
+		offloads |= 1ULL << VIRTIO_NET_F_GUEST_CSUM;
+
+	return virtnet_set_guest_offloads(vi, offloads);
+}
+
  static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
  			   struct netlink_ext_ack *extack)
  {
@@ -1898,10 +1947,11 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
  	u16 xdp_qp = 0, curr_qp;
  	int i, err;
  
-	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO4) ||
-	    virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO6) ||
-	    virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_ECN) ||
-	    virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_UFO)) {
+	if (!virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS)
+	    && (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO4) ||
+	        virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO6) ||
+	        virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_ECN) ||
+		virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_UFO))) {
  		NL_SET_ERR_MSG_MOD(extack, "Can't set XDP while host is implementing LRO, disable LRO first");
  		return -EOPNOTSUPP;
  	}
@@ -1950,6 +2000,12 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
  	for (i = 0; i < vi->max_queue_pairs; i++) {
  		old_prog = rtnl_dereference(vi->rq[i].xdp_prog);
  		rcu_assign_pointer(vi->rq[i].xdp_prog, prog);
+		if (i == 0) {
+			if (!old_prog)
+				virtnet_clear_guest_offloads(vi);
+			if (!prog)
+				virtnet_restore_guest_offloads(vi);
+		}
  		if (old_prog)
  			bpf_prog_put(old_prog);
  		napi_enable(&vi->rq[i].napi);
@@ -2583,6 +2639,10 @@ static int virtnet_probe(struct virtio_device *vdev)
  		netif_carrier_on(dev);
  	}
  
+	for (i = 0; i < ARRAY_SIZE(guest_offloads); i++)
+		if (virtio_has_feature(vi->vdev, guest_offloads[i]))
+			set_bit(guest_offloads[i], &vi->guest_offloads);
+
  	pr_debug("virtnet: registered device %s with %d RX and TX vq's\n",
  		 dev->name, max_queue_pairs);
  
@@ -2679,7 +2739,7 @@ static struct virtio_device_id id_table[] = {
  	VIRTIO_NET_F_CTRL_RX, VIRTIO_NET_F_CTRL_VLAN, \
  	VIRTIO_NET_F_GUEST_ANNOUNCE, VIRTIO_NET_F_MQ, \
  	VIRTIO_NET_F_CTRL_MAC_ADDR, \
-	VIRTIO_NET_F_MTU
+	VIRTIO_NET_F_MTU, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS
  
  static unsigned int features[] = {
  	VIRTNET_FEATURES,
--
2.7.4

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