Re: gso: Handle new frag_list of frags GRO packets

Herbert Xu
2013-11-13T14:26:24Z

On Tue, Nov 12, 2013 at 06:45:04PM -0800, Eric Dumazet wrote:
> On Wed, 2013-11-13 at 10:25 +0800, Herbert Xu wrote:
>
> > So a better test for the time being would be to test with TSO
> > disabled in both cases.
> >
>
> GRO on, TSO off, little difference between two cases :
>
> (Note some small things run in background, so these numbers are not
> ultra precise)

OK looks pretty sane.

> > In the mean time I'm cooking up a patch to generate TSO packets.
>
> That would be very nice !

It's failing on my machine but I'm not certain whether it's a bug
in my patch or a bug in my NIC's TSO code. So I'd appreciate it
if you can give this a spin on your mlx4.

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 557e1a5..1302515 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2786,6 +2786,8 @@ struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features)
__be16 proto;
bool csum;
int sg = !!(features & NETIF_F_SG);
+ int gso_type = 0;
+ int gso_size = 0;
int nfrags = skb_shinfo(skb)->nr_frags;
int err = -ENOMEM;
int i = 0;
@@ -2795,6 +2797,11 @@ struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features)
if (unlikely(!proto))
return ERR_PTR(-EINVAL);

+ if (net_gso_ok(gso_type, features)) {
+ gso_type = skb_shinfo(skb)->gso_type & ~SKB_GSO_DODGY;
+ gso_size = mss;
+ }
+
csum = !!can_checksum_protocol(features, proto);
__skb_push(skb, doffset);
headroom = skb_headroom(skb);
@@ -2807,7 +2814,7 @@ struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features)
int size;

len = skb->len - offset;
- if (len > mss)
+ if (!gso_size && len > mss)
len = mss;

hsize = skb_headlen(skb) - offset;
@@ -2819,6 +2826,26 @@ struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features)
if (!hsize && i >= nfrags && skb_headlen(fskb) &&
(skb_headlen(fskb) == len || sg)) {
BUG_ON(skb_headlen(fskb) > len);
+ SKB_FRAG_ASSERT(fskb);
+
+ nskb = skb_clone(fskb, GFP_ATOMIC);
+ if (unlikely(!nskb))
+ goto err;
+
+ if (gso_size) {
+ len = nskb->len;
+ pos += len;
+
+ skb_shinfo(nskb)->gso_segs = len / mss;
+
+ /*
+ * Original GRO packet boundaries must
+ * have been preserved.
+ */
+ BUG_ON(fskb->next && len % mss);
+
+ goto skip_trim;
+ }

i = 0;
nfrags = skb_shinfo(fskb)->nr_frags;
@@ -2837,17 +2864,14 @@ struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features)
skb_frag++;
}

- nskb = skb_clone(fskb, GFP_ATOMIC);
- fskb = fskb->next;
-
- if (unlikely(!nskb))
- goto err;
-
if (unlikely(pskb_trim(nskb, len))) {
kfree_skb(nskb);
goto err;
}

+skip_trim:
+ fskb = fskb->next;
+
hsize = skb_end_offset(nskb);
if (skb_cow_head(nskb, doffset + headroom)) {
kfree_skb(nskb);
@@ -2880,6 +2904,9 @@ struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features)

skb_headers_offset_update(nskb, skb_headroom(nskb) - headroom);

+ skb_shinfo(nskb)->gso_size = gso_size;
+ skb_shinfo(nskb)->gso_type = gso_type;
+
skb_copy_from_linear_data_offset(skb, -tnl_hlen,
nskb->data - tnl_hlen,
doffset + tnl_hlen);
@@ -2902,6 +2929,41 @@ struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features)

skb_shinfo(nskb)->tx_flags = skb_shinfo(skb)->tx_flags & SKBTX_SHARED_FRAG;

+ /*
+ * virtio-net misery:
+ *
+ * Do a trial run for hardware GSO to get the proper length.
+ */
+ if (pos < offset + len && gso_size) {
+ int j;
+
+ len = hsize - (offset - pos);
+
+ for (j = i; j < nfrags; j++)
+ len += skb_frag_size(skb_frag + j);
+
+ if (fskb && !skb_headlen(fskb)) {
+ j = min_t(int,
+ skb_shinfo(fskb)->nr_frags,
+ MAX_SKB_FRAGS - nfrags + i);
+
+ while (--j >= 0)
+ len += skb_frag_size(
+ skb_shinfo(fskb)->frags + j);
+ }
+
+ if (len < mss && offset + len < skb->len)
+ goto too_many_frags;
+
+ skb_shinfo(nskb)->gso_segs = len / mss;
+ if (len % mss) {
+ if (offset + len >= skb->len)
+ skb_shinfo(nskb)->gso_segs++;
+ else
+ len -= len % mss;
+ }
+ }
+
while (pos < offset + len) {
if (i >= nfrags) {
BUG_ON(skb_headlen(fskb));
@@ -2917,6 +2979,7 @@ struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features)

if (unlikely(skb_shinfo(nskb)->nr_frags >=
MAX_SKB_FRAGS)) {
+too_many_frags:
net_warn_ratelimited(
"skb_segment: too many frags: %u %u\n",
pos, mss);

Thanks!
--
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt