netdev - Re: [PATCH 5/7] xen-netfront: reduce gso_max_size to account for ethernet header

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Message-ID: <1365773815.15783.44.camel@zakaz.uk.xensource.com>
Date:	Fri, 12 Apr 2013 14:36:55 +0100
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Wei Liu <wei.liu2@...rix.com>
CC:	Eric Dumazet <eric.dumazet@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	David Vrabel <david.vrabel@...rix.com>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	"annie.li@...cle.com" <annie.li@...cle.com>,
	"wdauchy@...il.com" <wdauchy@...il.com>
Subject: Re: [PATCH 5/7] xen-netfront: reduce gso_max_size to account for
 ethernet header

On Fri, 2013-04-12 at 14:29 +0100, Wei Liu wrote:
> On Fri, Apr 12, 2013 at 01:58:19PM +0100, Eric Dumazet wrote:
> > On Fri, 2013-04-12 at 10:43 +0100, Ian Campbell wrote:
> > > On Fri, 2013-04-12 at 10:34 +0100, Wei Liu wrote:
> > 
> > > > But we don't have handle on this. If I understand correctly the
> > > > discussion in other thread, 90 is empirical value, not something
> > > > documented.
> > > 
> > > My original question was effectively "is anyone else going to be
> > > interested in this empirical value", if so then it seems like it would
> > > be useful to have it centrally defined.
> > > 
> > 
> > This could be MAX_TCP_HEADER. Probably a bit overestimated but do we
> > care ?
> > 
> 
> I don't think we care. MAX_TCP_HEADER is as good as any. Reserving a few
> more bytes won't hurt. I just want to make sure the value doesn't look
> like something randomly comes up in my mind. :-)
> 
> Ian, what do you think?

It could be up to 256 bytes from the looks of things, depending
on .config. That's probably ok.

Ian.


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