netdev - RE: Netxen packet loss with VLANs and LRO (was: [PATCH] netxen: fix LRO disable warning)

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Date:	Tue, 5 Apr 2011 08:15:16 -0500
From:	Amit Salecha <amit.salecha@...gic.com>
To:	Marc Haber <mh+netdev@...schlus.de>
CC:	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Ameen Rahman <ameen.rahman@...gic.com>,
	Rajesh Borundia <rajesh.borundia@...gic.com>
Subject: RE: Netxen packet loss with VLANs and LRO (was: [PATCH] netxen:	fix
 LRO disable warning)

> On Tue, Apr 05, 2011 at 12:38:11AM -0500, Amit Salecha wrote:
> > > On Mon, Mar 21, 2011 at 03:37:08AM -0700, Amit Kumar Salecha wrote:
> > > > netxen_nic_set_flags() rejects data if other flag than
> ETH_FLAG_LRO
> > > is set.
> > > > Driver also supports NETIF_F_HW_VLAN_TX.
> > > > Now compare data with ethtool_op_get_flags(), to get all
> supported
> > > features.
> > >
> > > Could that be the cause for packet loss on kernel 2.6.38.2 if:
> > >
> > >   - receiving card is NX3031 [4040:0100]
> > >   - frames are received with VLAN tags
> > >   - large received offload is on.
> >
> > If ip_forwarding or routing is enable ....then you may see packet
> loss.
>
> The box is intended to route, so disabling routing is
> contraproductive. I just would like to download software updates to
> the box with decent speed as well.

What I meant, with LRO enable and routing, you may see packet loss.
>
> > > Packet Loss of this kind is noticed when doing TCP data transfers
> > > towards the host with the Netxen Interface and the TCP session is
> > > terminated on the Netxen host itself. TCP sessions routed through
> the
> > > Netxen host are not affected.
> > >
> > > My ethtool doesn't allow me to influence the LRO setting alone - it
> is
> > > disabled when I set rx off but doesn't come on again when rx is set
> to
> > > on again. So, ethtool -K rx off, ethtool -K rx on fixes the issue.
> > >
> > If rx csum is disabled, LRO will be disable. LRO won't be enabled
> automatically if you enable rx csum.
> > You need to explicitly enable LRO.
>
> Explicitly enabling LRO does not work ("invalid argument", if I recall
> correctly).
>

With below patch enabling/disabling LRO will work.

> > > Is this a known bug, maybe with an available patch?
> > >
> > You need to retest with this patch
> > http://patchwork.ozlabs.org/patch/88060/. This patch got applied
> > instead of mine.
>
> Will that patch fix the behavior of the interface regarding the packet
> loss, or only its connection to ethtool?
>
This will fix LRO configuration problem. Do you see packet loss with LRO disable ?

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