Re: [PATCH net-next v6] gso: Support partial splitting at the frag_list pointer

[David Miller]

From: Alexander Duyck 
Date: Mon, 19 Sep 2016 08:12:15 -0700

> On Mon, Sep 19, 2016 at 3:58 AM, Steffen Klassert
>  wrote:
>> Since commit 8a29111c7 ("net: gro: allow to build full sized skb")
>> gro may build buffers with a frag_list. This can hurt forwarding
>> because most NICs can't offload such packets, they need to be
>> segmented in software. This patch splits buffers with a frag_list
>> at the frag_list pointer into buffers that can be TSO offloaded.
>>
>> Signed-off-by: Steffen Klassert 
 ...
> 
> Looks good.
> 
> Acked-by: Alexander Duyck 

Applied, thanks everyone.

Re: [PATCH net-next v6] gso: Support partial splitting at the frag_list pointer

[Alexander Duyck]

On Mon, Sep 19, 2016 at 3:58 AM, Steffen Klassert
 wrote:
> Since commit 8a29111c7 ("net: gro: allow to build full sized skb")
> gro may build buffers with a frag_list. This can hurt forwarding
> because most NICs can't offload such packets, they need to be
> segmented in software. This patch splits buffers with a frag_list
> at the frag_list pointer into buffers that can be TSO offloaded.
>
> Signed-off-by: Steffen Klassert 
> ---
>
> Changes since v1:
>
> - Use the assumption that all buffers in the chain excluding the last
>   containing the same amount of data.
>
> - Simplify some checks against gso partial.
>
> - Fix the generation of IP IDs.
>
> Changes since v2:
>
> - Merge common code of gso partial and frag_list pointer splitting.
>
> Changes since v3:
>
> - Fix the checks for doing frag_list pointer splitting.
>
> Changes since v4:
>
> - Whitespace fix.
> - Fix size calculations of the tail packet.
>
> Changes since v5:
>
> - Fix another size calculations of the tail packet.
>
>
>  net/core/skbuff.c  | 51 
> +++---
>  net/ipv4/af_inet.c | 14 ++
>  net/ipv4/gre_offload.c |  6 --
>  net/ipv4/tcp_offload.c | 13 +++--
>  net/ipv4/udp_offload.c |  6 --
>  net/ipv6/ip6_offload.c |  5 -
>  6 files changed, 69 insertions(+), 26 deletions(-)

Looks good.

Acked-by: Alexander Duyck 

[PATCH net-next v6] gso: Support partial splitting at the frag_list pointer

[Steffen Klassert]

Since commit 8a29111c7 ("net: gro: allow to build full sized skb")
gro may build buffers with a frag_list. This can hurt forwarding
because most NICs can't offload such packets, they need to be
segmented in software. This patch splits buffers with a frag_list
at the frag_list pointer into buffers that can be TSO offloaded.

Signed-off-by: Steffen Klassert 
---

Changes since v1:

- Use the assumption that all buffers in the chain excluding the last
  containing the same amount of data.

- Simplify some checks against gso partial.

- Fix the generation of IP IDs.

Changes since v2:

- Merge common code of gso partial and frag_list pointer splitting.

Changes since v3:

- Fix the checks for doing frag_list pointer splitting.

Changes since v4:

- Whitespace fix.
- Fix size calculations of the tail packet.

Changes since v5:

- Fix another size calculations of the tail packet.


 net/core/skbuff.c  | 51 +++---
 net/ipv4/af_inet.c | 14 ++
 net/ipv4/gre_offload.c |  6 --
 net/ipv4/tcp_offload.c | 13 +++--
 net/ipv4/udp_offload.c |  6 --
 net/ipv6/ip6_offload.c |  5 -
 6 files changed, 69 insertions(+), 26 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 1e329d4..7bf82a2 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3097,11 +3097,31 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
sg = !!(features & NETIF_F_SG);
csum = !!can_checksum_protocol(features, proto);
 
-   /* GSO partial only requires that we trim off any excess that
-* doesn't fit into an MSS sized block, so take care of that
-* now.
-*/
-   if (sg && csum && (features & NETIF_F_GSO_PARTIAL)) {
+   if (sg && csum && (mss != GSO_BY_FRAGS))  {
+   if (!(features & NETIF_F_GSO_PARTIAL)) {
+   struct sk_buff *iter;
+
+   if (!list_skb ||
+   !net_gso_ok(features, 
skb_shinfo(head_skb)->gso_type))
+   goto normal;
+
+   /* Split the buffer at the frag_list pointer.
+* This is based on the assumption that all
+* buffers in the chain excluding the last
+* containing the same amount of data.
+*/
+   skb_walk_frags(head_skb, iter) {
+   if (skb_headlen(iter))
+   goto normal;
+
+   len -= iter->len;
+   }
+   }
+
+   /* GSO partial only requires that we trim off any excess that
+* doesn't fit into an MSS sized block, so take care of that
+* now.
+*/
partial_segs = len / mss;
if (partial_segs > 1)
mss *= partial_segs;
@@ -3109,6 +3129,7 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
partial_segs = 0;
}
 
+normal:
headroom = skb_headroom(head_skb);
pos = skb_headlen(head_skb);
 
@@ -3300,21 +3321,29 @@ perform_csum_check:
 */
segs->prev = tail;
 
-   /* Update GSO info on first skb in partial sequence. */
if (partial_segs) {
+   struct sk_buff *iter;
int type = skb_shinfo(head_skb)->gso_type;
+   unsigned short gso_size = skb_shinfo(head_skb)->gso_size;
 
/* Update type to add partial and then remove dodgy if set */
-   type |= SKB_GSO_PARTIAL;
+   type |= (features & NETIF_F_GSO_PARTIAL) / NETIF_F_GSO_PARTIAL 
* SKB_GSO_PARTIAL;
type &= ~SKB_GSO_DODGY;
 
/* Update GSO info and prepare to start updating headers on
 * our way back down the stack of protocols.
 */
-   skb_shinfo(segs)->gso_size = skb_shinfo(head_skb)->gso_size;
-   skb_shinfo(segs)->gso_segs = partial_segs;
-   skb_shinfo(segs)->gso_type = type;
-   SKB_GSO_CB(segs)->data_offset = skb_headroom(segs) + doffset;
+   for (iter = segs; iter; iter = iter->next) {
+   skb_shinfo(iter)->gso_size = gso_size;
+   skb_shinfo(iter)->gso_segs = partial_segs;
+   skb_shinfo(iter)->gso_type = type;
+   SKB_GSO_CB(iter)->data_offset = skb_headroom(iter) + 
doffset;
+   }
+
+   if (tail->len - doffset <= gso_size)
+   skb_shinfo(tail)->gso_size = 0;
+   else if (tail != segs)
+   skb_shinfo(tail)->gso_segs = DIV_ROUND_UP(tail->len - 
doffset, gso_size);
}
 
/* Following permits correct backpressure, for protocols
diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index