netdev - Re: [PATCH 4/4] USBNET: ax88179_178a: enable tso if host supports sg dma

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Date:	Thu, 01 Aug 2013 06:21:40 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Oliver Neukum <oneukum@...e.de>,
	Freddy Xin <freddy@...x.com.tw>,
	Ben Hutchings <bhutchings@...arflare.com>,
	Grant Grundler <grundler@...gle.com>, netdev@...r.kernel.org,
	linux-usb@...r.kernel.org
Subject: Re: [PATCH 4/4] USBNET: ax88179_178a: enable tso if host supports
 sg dma

On Thu, 2013-08-01 at 16:10 +0800, Ming Lei wrote:
> On Thu, Aug 1, 2013 at 1:04 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > On Thu, 2013-08-01 at 12:41 +0800, Ming Lei wrote:
> >
> >> From my trace result, lots of linear SKBs are cloned or header-cloned, so
> >> it needs skb copy too.
> >>
> >> Is it normal in xmit path to see cloned SKBs for driver? If not, I can add check
> >> to avoid allocation of 8 bytes header for non-cloned skb.
> >
> > Existing code is not very friendly and very complex.
> >
> > Sure TCP stack does a clone for every skb from socket write queue,
> > but header should be available for pushing 8 bytes.
> >
> > The !skb_cloned(skb) test should be removed if the memmove() is not
> > needed.
> >
> > Could you try following patch ?
> 
> Tested-by: Ming Lei <ming.lei@...onical.com>
> 
> This patch does work, and it will make the patch 4/4 become very
> simple, :-)
> 
> I will rewrite this one against your patch.

OK I'll post an official patch then. I presume you got performance
increase, since we no longer do a copy of the TCP packets.



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