netdev - Re: Stable regression with 'tcp: allow splice() to build full TSO packets'

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Date:	Thu, 17 May 2012 18:33:24 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Willy Tarreau <w@....eu>
Cc:	netdev@...r.kernel.org
Subject: Re: Stable regression with 'tcp: allow splice() to build full TSO
 packets'

On Thu, 2012-05-17 at 17:56 +0200, Willy Tarreau wrote:
> On Thu, May 17, 2012 at 05:43:00PM +0200, Eric Dumazet wrote:

> It's the NIC included in the system-on-chip (Marvell 88F6281), and the NIC
> driver is mv643xx. It's the same hardware you find in sheevaplugs, guruplugs,
> dreamplugs and almost all ARM-based cheap NAS boxes.
> 
> > With commit 1d0c0b328a6 in net-next
> > (net: makes skb_splice_bits() aware of skb->head_frag)
> > You'll be able to get even more speed, if NIC uses frag to hold frame.
> 
> I'm going to check this now, sounds interesting :-)

splice(socket -> pipe) does a copy of frame from skb->head to a page
fragment.

With latest patches (net-next), we can provide a frag for skb->head and
avoid this copy in splice(). You would have a true zero copy
socket->socket mode.

tg3 drivers uses this new thing, mv643xx_eth.c could be changed as well.



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