From mboxrd@z Thu Jan  1 00:00:00 1970
From: Roland Dreier <rdreier@cisco.com>
Subject: Re: Question regarding protocol specific mtu for FCoE
Date: Wed, 03 Jun 2009 14:21:11 -0700
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In-Reply-To: <4A26E4AE.4020607@hp.com> (Rick Jones's message of "Wed, 03 Jun
	2009 14:01:34 -0700")
Sender: netdev-owner@vger.kernel.org
To: Rick Jones <rick.jones2@hp.com>
Cc: "Zou, Yi" <yi.zou@intel.com>, "netdev@vger.kernel.org" <netdev@vger.kernel.org>, "linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>, "Leech, Christopher" <christopher.leech@intel.com>, "Dev, Vasu" <vasu.dev@intel.com>, "Love, Robert W" <robert.w.love@intel.com>, "Ma, Steve" <steve.ma@intel.com>, "Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@intel.com>, "Kirsher, Jeffrey T" <jeffrey.t.kirsher@intel.com>
List-Id: linux-scsi@vger.kernel.org

 > So FCoE cannot say "fcoe_mtu = min(OPTIMAL_FCOEMTU,netdev->mtu)" and
 > send-down frames based on that?

I think the point is that FCoE wants to use OPTIMAL_FCOEMTU (2KB + a bit
for headers) even when netdev->mtu is 1500.  (eg datacenter network
supports baby jumbo frames so FCoE traffic that stays within the network
should use OPTIMAL_FCOEMTU, while lots of IP traffic is going out onto a
1500-byte MTU campus and having TCP doing lots of PMTU discovery is a
pain)

 - R.