netdev - Re: [PATCH 2/2] IB/ipoib: fix GRO merge failure for IPoIB originated TCP streams

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Date:	Thu, 02 Feb 2012 15:38:15 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Or Gerlitz <ogerlitz@...lanox.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

Le jeudi 02 février 2012 à 16:01 +0200, Or Gerlitz a écrit :
> 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?

I guess changing hard_header_len might be difficult (for you).

Adding gro_mac_header_len sounds the easy way.

[ You'll need to set it in your device setup() ]




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