linux-kernel - Re: RFC: MTU for serving NFS on Infiniband

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Message-ID: <1282672647.2302.15.camel@achroite.uk.solarflarecom.com>
Date:	Tue, 24 Aug 2010 18:57:27 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Marc Aurele La France <tsi@...berta.ca>
Cc:	Stephen Hemminger <shemminger@...tta.com>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	"Pekka Savola (ipv6)" <pekkas@...core.fi>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: RFC: MTU for serving NFS on Infiniband

On Tue, 2010-08-24 at 09:14 -0600, Marc Aurele La France wrote:
> On Mon, 23 Aug 2010, Stephen Hemminger wrote:
> > On Mon, 23 Aug 2010 08:44:37 -0600 (MDT)
> > Marc Aurele La France <tsi@...berta.ca> wrote:
> >> In regrouping for my next tack at this, I noticed that all stack traces go
> >> through ip_append_data().  This would be ipv6_append_data() in the IPv6 case.
> >> A _very_ rough draft that would have ip_append_data() temporarily drop down
> >> to a smaller fake MTU follows ...
> 
> > Why doesn't NFS generate page size fragments?  Does Infiniband or your
> > device not support this?  Any thing that requires higher order allocation
> > is going to unstable under load.  Let's fix the cause not the apply bandaid
> > solution to the symptom.
> 
> From what I can tell, IP fragmentation is done centrally.
[...]

Stephen and I are not talking about IP fragmentation, but about the
ability to append 'fragments' to an skb rather than putting the entire
packet payload in a linear buffer.  See
<http://vger.kernel.org/~davem/skb_data.html>.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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