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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: Thomas Graf <tgraf@suug.ch>
Signed-off-by: Jesse Gross <jesse@nicira.com>
This commit is contained in:
Thomas Graf 2013-12-13 15:22:21 +01:00 committed by Jesse Gross
parent 8055a89cfa
commit bda56f143c
1 changed files with 29 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

37
net/openvswitch/datapath.c
View File

@ -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);
((struct nlmsghdr *) user_skb->data)->nlmsg_len = user_skb->len;
genlmsg_end(user_skb, upcall);
err = genlmsg_unicast(ovs_dp_get_net(dp), user_skb, upcall_info->portid);
out:
kfree_skb(nskb);
return err;