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Commit bda56f14 authored by Thomas Graf's avatar Thomas Graf Committed by Jesse Gross
Browse files

openvswitch: Use skb_zerocopy() for upcall 



Use of skb_zerocopy() can avoid the expensive call to memcpy()
when copying the packet data into the Netlink skb. Completes
checksum through skb_checksum_help() if not already done in
GSO segmentation.

Zerocopy is only performed if user space supported unaligned
Netlink messages. memory mapped netlink i/o is preferred over
zerocopy if it is set up.

Cost of upcall is significantly reduced from:
+   7.48%       vhost-8471  [k] memcpy
+   5.57%     ovs-vswitchd  [k] memcpy
+   2.81%       vhost-8471  [k] csum_partial_copy_generic

to:
+   5.72%     ovs-vswitchd  [k] memcpy
+   3.32%       vhost-5153  [k] memcpy
+   0.68%       vhost-5153  [k] skb_zerocopy

(megaflows disabled)

Signed-off-by: default avatarThomas Graf <tgraf@suug.ch>
Signed-off-by: default avatarJesse Gross <jesse@nicira.com>
parent 8055a89c

net/openvswitch/datapath.c

+29 −8
Original line number Diff line number Diff line
@@ -371,11 +371,11 @@ static size_t key_attr_size(void) 
		+ nla_total_size(28); /* OVS_KEY_ATTR_ND */

}



static size_t upcall_msg_size(const struct sk_buff *skb,

			      const struct nlattr *userdata)

static size_t upcall_msg_size(const struct nlattr *userdata,

			      unsigned int hdrlen)

{

	size_t size = NLMSG_ALIGN(sizeof(struct ovs_header))

		+ nla_total_size(skb->len) /* OVS_PACKET_ATTR_PACKET */

		+ nla_total_size(hdrlen) /* OVS_PACKET_ATTR_PACKET */

		+ nla_total_size(key_attr_size()); /* OVS_PACKET_ATTR_KEY */



	/* OVS_PACKET_ATTR_USERDATA */
@@ -397,6 +397,7 @@ static int queue_userspace_packet(struct datapath *dp, struct sk_buff *skb, 
		.snd_portid = upcall_info->portid,

	};

	size_t len;

	unsigned int hlen;

	int err, dp_ifindex;



	dp_ifindex = get_dpifindex(dp);
@@ -421,7 +422,21 @@ static int queue_userspace_packet(struct datapath *dp, struct sk_buff *skb, 
		goto out;

	}



	len = upcall_msg_size(skb, upcall_info->userdata);

	/* Complete checksum if needed */

	if (skb->ip_summed == CHECKSUM_PARTIAL &&

	    (err = skb_checksum_help(skb)))

		goto out;



	/* Older versions of OVS user space enforce alignment of the last

	 * Netlink attribute to NLA_ALIGNTO which would require extensive

	 * padding logic. Only perform zerocopy if padding is not required.

	 */

	if (dp->user_features & OVS_DP_F_UNALIGNED)

		hlen = skb_zerocopy_headlen(skb);

	else

		hlen = skb->len;



	len = upcall_msg_size(upcall_info->userdata, hlen);

	user_skb = genlmsg_new_unicast(len, &info, GFP_ATOMIC);

	if (!user_skb) {

		err = -ENOMEM;
@@ -441,13 +456,19 @@ static int queue_userspace_packet(struct datapath *dp, struct sk_buff *skb, 
			  nla_len(upcall_info->userdata),

			  nla_data(upcall_info->userdata));



	nla = __nla_reserve(user_skb, OVS_PACKET_ATTR_PACKET, skb->len);

	/* Only reserve room for attribute header, packet data is added

	 * in skb_zerocopy() */

	if (!(nla = nla_reserve(user_skb, OVS_PACKET_ATTR_PACKET, 0))) {

		err = -ENOBUFS;

		goto out;

	}

	nla->nla_len = nla_attr_size(skb->len);



	skb_copy_and_csum_dev(skb, nla_data(nla));

	skb_zerocopy(user_skb, skb, skb->len, hlen);



	genlmsg_end(user_skb, upcall);

	err = genlmsg_unicast(ovs_dp_get_net(dp), user_skb, upcall_info->portid);

	((struct nlmsghdr *) user_skb->data)->nlmsg_len = user_skb->len;



	err = genlmsg_unicast(ovs_dp_get_net(dp), user_skb, upcall_info->portid);

out:

	kfree_skb(nskb);

	return err;