netdev - Re: [PATCH] tcp: Set CHECKSUM_UNNECESSARY in tcp_init_nondata

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Date:	Thu, 08 Apr 2010 11:34:20 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	herbert@...dor.apana.org.au
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] tcp: Set CHECKSUM_UNNECESSARY in tcp_init_nondata_skb

From: Herbert Xu <herbert@...dor.apana.org.au>
Date: Thu, 8 Apr 2010 23:39:06 +0800

> On Thu, Apr 08, 2010 at 09:57:15PM +0800, Herbert Xu wrote:
>> 
>> The problem here is that for non-data packets CHECKSUM_PARTIAL
>> can actually end up being worse if we wind up going out through
>> an interface that doesn't support checksums.
> 
> I don't know what I was thinking but the above is totally wrong.
> CHECKSUM_PARTIAL should be just fine on non-checksuming interfaces
> as we'll checksum everything once just as the CHECKSUM_NONE case
> would.
> 
> So with that in mind, we don't need my CHECKSUM_UNNECESSARY patch
> at all and your CHECKSUM_PARTIAL path is the right solution after
> all :)

Ok, thanks for doing all of the analysis :)

That still leaves that MC loopback code in ip_dev_loopback_xmit()
which still sets CHECKSUM_UNNECESSARY unconditionally.

Should it do like the loopback driver and just leave the ip_summed
value alone?
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