netdev - Re: [PATCH net-next] bnx2x: Disable LRO on FCoE or iSCSI boot device

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Date:	Fri, 14 Oct 2011 13:59:58 -0700
From:	"Michael Chan" <mchan@...adcom.com>
To:	"John Fastabend" <john.r.fastabend@...el.com>
cc:	"'Rick Jones'" <rick.jones2@...com>,
	"'davem@...emloft.net'" <davem@...emloft.net>,
	"'netdev@...r.kernel.org'" <netdev@...r.kernel.org>,
	"Dmitry Kravkov" <dmitry@...adcom.com>,
	"Eilon Greenstein" <eilong@...adcom.com>, eddie.wai@...adcom.com
Subject: Re: [PATCH net-next] bnx2x: Disable LRO on FCoE or iSCSI boot
 device


On Fri, 2011-10-14 at 13:17 -0700, John Fastabend wrote:
> On 10/14/2011 9:15 AM, Michael Chan wrote:
> > Rick Jones wrote:
> > 
> >> On 10/14/2011 08:53 AM, Michael Chan wrote:
> >>> Rick Jones wrote:
> >>>
> >>>> Is this perhaps saying that a bnx2x-driven device being used for
> >>>> FCoE or iSCSI boot must not permit *any* run-time configuration
> >>>> change which leads to a NIC reset?
> >>>>
> >>>
> >>> That is right.  Unless you have a multipath configuration with
> >> multiple
> >>> ports, then you can reset one port at a time.
> >>
> >> So, should there also be a "cnic_boot_device" check in many of the
> >> "capital letter" ethtool paths?
> >>
> > 
> > If the user is doing ethtool configuration changes or device shutdown,
> > it is more obvious what the consequence will be.  The user may also be
> > careful to do it on a multipath setup.
> > 
> > The reset caused by the auto turn-off of LRO when you enable
> > ip_forward or bridging will not be obvious to the user.  In addition,
> > all devices with LRO turned on will be reset at the same time so even
> > multipath will not survive.
> >
> 
> But after the reset the device should login and SCSI layer should
> handle retries. So I don't see why this is a problem. Why do we
> need to handle this any different from any other link events?
> 

During a link down event, the iSCSI state does not get reset.  When link
comes back up quickly enough, there should be just some retransmissions
and everything should recover.  The root file system won't tolerate a
chip reset that will reset the iSCSI state.


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