netdev - RE: [RFC] r8169 : why SG / TX checksum are default disabled

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Date:	Fri, 20 Jul 2012 15:14:26 +0800
From:	hayeswang <hayeswang@...ltek.com>
To:	'David Miller' <davem@...emloft.net>, <eric.dumazet@...il.com>
CC:	<romieu@...zoreil.com>, <netdev@...r.kernel.org>
Subject: RE: [RFC] r8169 : why SG / TX checksum are default disabled

 Francois Romieu <romieu@...zoreil.com>

> >> > A NETDEV_TX_OK return means we accepted the SKB, it 
> doesn't look like
> >> > that's what you are doing in the skb_padto() failure path.
> >> 
> >> ?
> >> 
> >> - skb_padto fails
> >>   (original skb is implicitely freed)
> >> - skb_padto returns error status (!= 0)
> >> - rtl8169_tso_csum returns false
> >> - start_xmit returns NETDEV_TX_OK. 
> >> 
> >> I'll search the missing "!" after some sleep if that's 
> what you are talking
> >> about. Otherwise than that, I don't get it.
> >> 
> > 
> > 
> > Yes, I believe your patch is fine.
> > 
> > In fact many drivers dont account the error in their stats.
> 
> My bad, I forgot that skb_padto() frees the SKB on failure.
> 

I find that the total length field of IP header would be modified if the hw
checksum is enabled. Therefore, skb_padto + hw checksum wouldn't work. The
software checksum is necessary.
 
Best Regards,
Hayes

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