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Date:	Thu, 13 Sep 2012 15:22:12 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Or Gerlitz <or.gerlitz@...il.com>
Cc:	Shlomo Pongartz <shlomop@...lanox.com>,
	Rick Jones <rick.jones2@...com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Tom Herbert <therbert@...gle.com>,
	Yevgeny Petrilin <yevgenyp@...lanox.co.il>
Subject: Re: GRO aggregation

On Thu, 2012-09-13 at 15:47 +0300, Or Gerlitz wrote:
> Shlomo is dealing with making the IPoIB driver work well with GRO,
> thanks for the
> comments on the Mellanox Ethernet driver, we will look there too
> (added Yevgeny)...
> 
> As for IPoIB it has two modes, connected which irrelevant for this
> discussion, and datagram
> - who is under the  scope here. Its MTU is typically 2044 but can be
> 4092 as well, the allocation
> of skb's for this mode is done in ipoib_alloc_rx_skb() -- which you've
> patched recently...
> 
> Following your comment we noted that if using the lower/typical mtu of
> 2044 which means
> we are below the ipoib_ud_need_sg() threshold, skbs are allocated on
> one "form" and if using
> the 4092 mtu in another "form" - do you see each of the form to fall
> into different GRO flow, e.g
> 2044 to the "slow" and 4092 to the "fast"?!

Seems fine to me both ways, because you use dev_alloc_skb(), and you
dont pull tcp payload into tcp->head.

You might try adding prefetch() as well to bring into cpu cache
IP/TCP headers before they are needed in gro layers.



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