[ovs-dev] [PATCH net-next 2/2] openvswitch: Use zerocopy if applicable when performing the upcall

[Thomas Graf]

From: Thomas Graf <tgraf@rhlap.localdomain>

Avoids a memcpy() that is expensive for large packets:

from:
  4.51%  [kernel]                      [k] memcpy
to:
  1.20%  [kernel]                      [k] memcpy
  1.01%  [kernel]                      [k] skb_zerocopy

Signed-off-by: Thomas Graf <tg...@suug.ch>
---
 net/openvswitch/datapath.c | 38 ++++++++++++++++++++++++++++++++------
 1 file changed, 32 insertions(+), 6 deletions(-)

diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c
index d12d6b8..b434adf 100644
--- a/net/openvswitch/datapath.c
+++ b/net/openvswitch/datapath.c
@@ -375,10 +375,11 @@ static size_t key_attr_size(void)
 }
 
 static size_t upcall_msg_size(const struct sk_buff *skb,
-                             const struct nlattr *userdata)
+                             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 */
@@ -396,6 +397,7 @@ static int queue_userspace_packet(struct net *net, int 
dp_ifindex,
        struct sk_buff *nskb = NULL;
        struct sk_buff *user_skb; /* to be queued to userspace */
        struct nlattr *nla;
+       unsigned int plen, hlen = 0;
        int err;
 
        if (vlan_tx_tag_present(skb)) {
@@ -416,7 +418,21 @@ static int queue_userspace_packet(struct net *net, int 
dp_ifindex,
                goto out;
        }
 
-       user_skb = genlmsg_new(upcall_msg_size(skb, upcall_info->userdata), 
GFP_ATOMIC);
+       if (skb->ip_summed == CHECKSUM_PARTIAL &&
+           (err = skb_checksum_help(skb)))
+               goto out;
+
+       if (!skb->head_frag ||
+           skb_headlen(skb) < L1_CACHE_BYTES ||
+           skb_shinfo(skb)->nr_frags >= MAX_SKB_FRAGS)
+               hlen = skb_headlen(skb);
+
+       if (skb_has_frag_list(skb))
+               hlen = skb->len;
+
+       hlen = min_t(int, skb->len, hlen);
+
+       user_skb = genlmsg_new(upcall_msg_size(skb, upcall_info->userdata, 
hlen), GFP_ATOMIC);
        if (!user_skb) {
                err = -ENOMEM;
                goto out;
@@ -435,11 +451,21 @@ static int queue_userspace_packet(struct net *net, int 
dp_ifindex,
                          nla_len(upcall_info->userdata),
                          nla_data(upcall_info->userdata));
 
-       nla = __nla_reserve(user_skb, OVS_PACKET_ATTR_PACKET, skb->len);
+       if (!(nla = nla_reserve(user_skb, OVS_PACKET_ATTR_PACKET, 0)))
+               goto out;
+       nla->nla_len = nla_attr_size(skb->len);
+
+       skb_zerocopy(user_skb, skb, skb->len, hlen);
 
-       skb_copy_and_csum_dev(skb, nla_data(nla));
+       plen = NLA_ALIGN(user_skb->len) - user_skb->len;
+       if (plen > 0)
+               memset(skb_put(user_skb, plen), 0, plen);
+
+       /* Fix alignment of .nlmsg_len, OVS user space enforces a strict
+        * total message size alignment.
+        */
+       ((struct nlmsghdr *) user_skb->data)->nlmsg_len = 
NLA_ALIGN(user_skb->len);
 
-       genlmsg_end(user_skb, upcall);
        err = genlmsg_unicast(net, user_skb, upcall_info->portid);
 
 out:
-- 
1.7.11.7

_______________________________________________
dev mailing list
dev@openvswitch.org
http://openvswitch.org/mailman/listinfo/dev