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Date: Thu, 2 Feb 2012 16:01:47 +0200
From: Or Gerlitz <ogerlitz@...lanox.com>
To: Eric Dumazet <eric.dumazet@...il.com>
CC: Herbert Xu <herbert@...dor.apana.org.au>,
Roland Dreier <roland@...nel.org>, <netdev@...r.kernel.org>,
linux-rdma <linux-rdma@...r.kernel.org>,
Shlomo Pongratz <shlomop@...lanox.com>
Subject: Re: [PATCH 2/2] IB/ipoib: fix GRO merge failure for IPoIB originated
TCP streams
On 2/1/2012 4:07 PM, Eric Dumazet wrote:
>>> If we just turn it into a memcmp with a variable length would
>>> that work for you?
>>
>> I think yes, FWIW we will compare the IPoIB header, Roland is that okay for you?
>
> A memcmp(xxx, yyy, variable_len) will be out of line and slow, its a bit sad ... Are skb_mac_header(p) / skb_gro_mac_header(skb) going to point to IPoIB header ?
yes, both skb_mac_header(p) / skb_gro_mac_header(skb) point to IPoIB
header, however (see next)
> Maybe we can keep a fastpath for ethernet case... (the "if (hlen == ETH_HLEN) being always predicted)
> Maybe need to introduce gro_hard_header_len as well)
today, IPoIB advertizes hard_header_len which is bigger than the IPoIB
header len, this is done such that skbs sent by the network stack have
enough headroom for a "pseudoheader" which for few flows (e.g unicast
arp replies and multicast) is placed there by the ipoib hard_header
function and later used by the xmit function.
So we can either try and change that, such that hard_header_len will be
equal to the ipoib header len or add gro_hard_header_len as you
suggested, any preferences?
Or.
Or.
>
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 115dee1..62abee4 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -3500,14 +3500,20 @@ static inline gro_result_t
> __napi_gro_receive(struct napi_struct *napi, struct sk_buff *skb)
> {
> struct sk_buff *p;
> + unsigned int hlen = skb->dev->hard_header_len;
>
> for (p = napi->gro_list; p; p = p->next) {
> unsigned long diffs;
>
> diffs = (unsigned long)p->dev ^ (unsigned long)skb->dev;
> diffs |= p->vlan_tci ^ skb->vlan_tci;
> - diffs |= compare_ether_header(skb_mac_header(p),
> - skb_gro_mac_header(skb));
> + if (hlen == ETH_HLEN)
> + diffs |= compare_ether_header(skb_mac_header(p),
> + skb_gro_mac_header(skb));
> + else if (!diffs)
> + diffs = memcmp(skb_mac_header(p),
> + skb_gro_mac_header(skb),
> + skb->dev->hard_header_len);
> NAPI_GRO_CB(p)->same_flow = !diffs;
> NAPI_GRO_CB(p)->flush = 0;
> }
>
>
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