netdev - Re: [PATCH] ipv6: udp packets following an UFO enqueued packet need also be handled by UFO

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Date:	Wed, 02 Oct 2013 08:14:27 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org,
	yoshfuji@...ux-ipv6.org, davem@...emloft.net, kuznet@....inr.ac.ru,
	jmorris@...ei.org, kaber@...sh.net, herbert@...dor.apana.org.au
Subject: Re: [PATCH] ipv6: udp packets following an UFO enqueued packet need
 also be handled by UFO

On Wed, 2013-10-02 at 15:03 +0200, Hannes Frederic Sowa wrote:
> On Wed, Oct 02, 2013 at 02:12:07PM +0200, Hannes Frederic Sowa wrote:
> > Hi Eric!
> > 
> > On Wed, Oct 02, 2013 at 03:41:28AM -0700, Eric Dumazet wrote:
> > > On Wed, 2013-10-02 at 10:58 +0200, Jiri Pirko wrote:
> > > > Wed, Oct 02, 2013 at 01:25:34AM CEST, hannes@...essinduktion.org wrote:
> > > > >-	if (((length > mtu) || (skb && skb_is_gso(skb))) &&
> > > > >+	if (((length > mtu) || (skb && skb_has_frags(skb))) &&
> > > 
> > > > 
> > > > This seems correct to me. sk_is_gso would work as well is you apply my
> > > > patch "[patch net] ip6_output: do skb ufo init for peeked non ufo skb as
> > > > well" which does the setting of gso_size.
> > > 
> > > Well, skb having frags or not should not be a concern :
> > > Thats an allocation choice (lets say to avoid high order allocations). 
> > > 
> > > Setting gso_size is probably better.
> > 
> > e89e9cf539a28df7d0eb1d0a545368e9920b34ac ("[IPv4/IPv6]: UFO Scatter-gather
> > approach") states:
> > 
> > "
> > skb->data will contain MAC/IP/UDP header and skb_shinfo(skb)->frags[]
> > contains the data payload. The skb->ip_summed will be set to CHECKSUM_HW
> > indicating that hardware has to do checksum calculation. Hardware should
> > compute the UDP checksum of complete datagram and also ip header checksum of
> > each fragmented IP packet.
> > "
> > 
> > This is the reason why I tried not to update the gso_size. If it is ok, I am
> > fine with that.
> 
> Especially, drivers/net/ethernet/neterion/s2io.c states that the first dma
> mapping (skb->data with skb_headlen, which is fine) is used as the inband
> header:
> 
>         if (offload_type == SKB_GSO_UDP)
>                 frg_cnt++; /* as Txd0 was used for inband header */
> 
> That is my only other hint that we maybe should not update gso_size and
> gso_type. I guess software fallback does not have this problem, but I won't
> have time to check until this evening.
> 
> I am really not sure if just setting gso_size does not break neterion UFO
> offloading. :/

Well, just ask Jon Mason to double check ;)

I think the commit intent was to set gso_size :

   skb_shinfo(skb)->ufo_size will indicate the length of data part in each IP
    fragment going out of the adapter after IP fragmentation by hardware.

The fact that it states "skb->data will contain MAC/IP/UDP header and
skb_shinfo(skb)->frags[] contains the data payload." seems irrelevant.

If Neterion driver mandates that skb->head *only* contains the
MAC/IP/UDP header, that should be handled in the driver itself.



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