netdev - Re: [PATCH 2/2] tcp: remove the sk_can_gso() check from tcp_set_skb_tso

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Date:	Thu, 17 Oct 2013 16:09:07 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, ncardwell@...gle.com, ycheng@...gle.com
Subject: Re: [PATCH 2/2] tcp: remove the sk_can_gso() check from
 tcp_set_skb_tso_segs()

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Tue, 15 Oct 2013 12:24:54 -0700

> From: Eric Dumazet <edumazet@...gle.com>
> 
> sk_can_gso() should only be used as a hint in tcp_sendmsg() to build GSO
> packets in the first place. (As a performance hint)
> 
> Once we have GSO packets in write queue, we can not decide they are no
> longer GSO only because flow now uses a route which doesn't handle
> TSO/GSO.
> 
> Core networking stack handles the case very well for us, all we need
> is keeping track of packet counts in MSS terms, regardless of
> segmentation done later (in GSO or hardware)
> 
> Right now, if  tcp_fragment() splits a GSO packet in two parts,
> @left and @right, and route changed through a non GSO device,
> both @left and @right have pcount set to 1, which is wrong,
> and leads to incorrect packet_count tracking.
> 
> This problem was added in commit d5ac99a648 ("[TCP]: skb pcount with MTU
> discovery")
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>

Also applied and queued up for -stable, thanks everyone.
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