netdev - Re: [PATCH] veth: remove hardware checksum feature

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Date:	Thu, 08 Aug 2013 12:43:34 -0700
From:	Ben Greear <greearb@...delatech.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	netdev@...r.kernel.org
Subject: Re: [PATCH] veth: remove hardware checksum feature

On 08/07/2013 07:52 PM, Eric Dumazet wrote:
> On Wed, 2013-08-07 at 18:54 -0700, Ben Greear wrote:
>
>> Maybe we should just do the csum calc in the kernel if packet is
>> about to be sent up to user-space via af_packet?  I think that
>> would keep the expected behaviour, and hopefully not loose any of the performance
>> benefits for cases where the packet never leaves the kernel?
>
> I think you are rephrasing what I suggested ;)
>
> I'll send a patch asap, unless someone beats me.

I'll be happy to test.

And a slightly related question if you have the time:

My kernel-mode bridge was breaking as well, but this appears to
be a bug in my code.  I had this code (since 2009, at least):

// Evidently this fixes issues with sending between NICs
// that support and do not support hw-csum.
skb->ip_summed = CHECKSUM_NONE;

It seems that at some point, this fixed some problem I saw, but it was long
ago.  If I remove this, then the 3.9 kernel bridges just fine between
the VETH and a physical interface.

I do not see any modification of the ip_summed in the bridge code.

So, the question is:  Is there any time that I *should* be mucking with
skb->ip_summed when bridging pkts from one device to another on modern
kernels?  I'm using the ptype_all hook to grab packets, and ndo_start_xmit
to send them, in case that matters.

Thanks,
Ben

-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com

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