netdev - Re: [PATCH] mac80211: rewrite fragmentation code

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Message-Id: <200805161201.48835.rusty@rustcorp.com.au>
Date:	Fri, 16 May 2008 12:01:48 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	David Miller <davem@...emloft.net>
Cc:	herbert@...dor.apana.org.au, mb@...sch.de,
	johannes@...solutions.net, linux-wireless@...r.kernel.org,
	netdev@...r.kernel.org, ron.rindjunsky@...el.com, tomasw@...il.com,
	ivdoorn@...il.com, peter.p.waskiewicz.jr@...el.com
Subject: Re: [PATCH] mac80211: rewrite fragmentation code

On Thursday 08 May 2008 13:26:06 David Miller wrote:
> From: Herbert Xu <herbert@...dor.apana.org.au>
> Date: Thu, 8 May 2008 11:22:08 +0800
>
> > On Wed, May 07, 2008 at 03:48:06PM +0200, Michael Buesch wrote:
> > > So there's no way to actually fail in a TX handler? Drivers
> > > are doomed to drop the packet, if they cannot handle it due to
> > > ring overflow?
> >
> > You're supposed to stop the queue before the ring overflows.
>
> Right, and this is why drivers choose a TX wakeup threshold such
> that they can accept an arbitrarily sized TSO frame.

Dave, please allow me to ask a heretical question.  Returning TX_BUSY has some 
appeal for virtio_net: is it fundamentally a flawed idea, or simply a matter 
of coding?

Currently we have no virtio interface to ask how many descriptors are left; 
it's not clear that it's a fair question to ask, since for Xen it's depends 
on the actual buffers we're trying to put in the descirptors.

Thanks,
Rusty.
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