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net: gro: remove obsolete code from skb_gro_receive() 

Some drivers use copybreak to copy tiny frames into smaller skb,
and this smaller skb might not have skb->head_frag set for various
reasons.

skb_gro_receive() currently doesn't allow to aggregate the smaller skb
into the previous GRO packet if this GRO packet has at least 2 MSS in
it.

Following workload easily demonstrates the problem.

netperf -t TCP_RR -H target -- -r 3000,3000

(tcpdump shows one GRO packet with 2 MSS, plus one additional packet of
104 bytes that should have been appended.)

It turns out that we can remove code from skb_gro_receive(), because
commit 8a29111c7c ("net: gro: allow to build full sized skb") and its
followups removed the assumption that a GRO packet with a frag_list had
to have an empty head.

Removing this code allows the aggregation of the last (incomplete) frame
in some RPC workloads. Note that tcp_gro_receive() already takes care of
forcing a flush if necessary, including this case.

If we want to avoid using frag_list in the first place (in forwarding
workloads for example, as the outgoing NIC is generally not able to cope
with skbs having a frag_list), we need to address this separately.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2015-03-05 13:47:48 -08:00 committed by David S. Miller
parent feb27d155d
commit 58025e46ea
1 changed files with 1 additions and 44 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

45
net/core/skbuff.c
View File

@ -3206,10 +3206,9 @@ int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb)
struct skb_shared_info *pinfo, *skbinfo = skb_shinfo(skb);
unsigned int offset = skb_gro_offset(skb);
unsigned int headlen = skb_headlen(skb);
struct sk_buff *nskb, *lp, *p = *head;
unsigned int len = skb_gro_len(skb);
struct sk_buff *lp, *p = *head;
unsigned int delta_truesize;
unsigned int headroom;
if (unlikely(p->len + len >= 65536))
return -E2BIG;
@ -3276,48 +3275,6 @@ int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb)
NAPI_GRO_CB(skb)->free = NAPI_GRO_FREE_STOLEN_HEAD;
goto done;
}
/* switch back to head shinfo */
pinfo = skb_shinfo(p);
if (pinfo->frag_list)
goto merge;
if (skb_gro_len(p) != pinfo->gso_size)
return -E2BIG;
headroom = skb_headroom(p);
nskb = alloc_skb(headroom + skb_gro_offset(p), GFP_ATOMIC);
if (unlikely(!nskb))
return -ENOMEM;
__copy_skb_header(nskb, p);
nskb->mac_len = p->mac_len;
skb_reserve(nskb, headroom);
__skb_put(nskb, skb_gro_offset(p));
skb_set_mac_header(nskb, skb_mac_header(p) - p->data);
skb_set_network_header(nskb, skb_network_offset(p));
skb_set_transport_header(nskb, skb_transport_offset(p));
__skb_pull(p, skb_gro_offset(p));
memcpy(skb_mac_header(nskb), skb_mac_header(p),
p->data - skb_mac_header(p));
skb_shinfo(nskb)->frag_list = p;
skb_shinfo(nskb)->gso_size = pinfo->gso_size;
pinfo->gso_size = 0;
__skb_header_release(p);
NAPI_GRO_CB(nskb)->last = p;
nskb->data_len += p->len;
nskb->truesize += p->truesize;
nskb->len += p->len;
*head = nskb;
nskb->next = p->next;
p->next = NULL;
p = nskb;
merge:
delta_truesize = skb->truesize;