netdev - Re: [PATCH 11/13] bnx2x: Forbid LRO on when XEN is enabled

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Message-ID: <20100419091446.39e2510c@nehalam>
Date:	Mon, 19 Apr 2010 09:14:46 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	David Miller <davem@...emloft.net>
Cc:	bhutchings@...arflare.com, vladz@...adcom.com, eilong@...adcom.com,
	netdev@...r.kernel.org, dmitry@...adcom.com
Subject: Re: [PATCH 11/13] bnx2x: Forbid LRO on when XEN is enabled

On Sun, 18 Apr 2010 20:58:58 -0700 (PDT)
David Miller <davem@...emloft.net> wrote:

> From: Ben Hutchings <bhutchings@...arflare.com>
> Date: Sun, 18 Apr 2010 16:11:25 +0100
> 
> > On Sun, 2010-04-18 at 17:50 +0300, Vladislav Zolotarov wrote:
> >> LRO cannot be used on virtualized environment, so it is best
> >> to disable it on compile time in XEN kernel.
> > [...]
> > 
> > If you want to cripple your performance, I'm not going to stand in your
> > way, but be aware that most distribution kernels now enable CONFIG_XEN.
> 
> There is also zero reason to do this.
> 
> When the XEN code or whatever setups up the bridge, LRO will be
> disabled by the bridge code.
> 
> It automatically issues ethtool LRO disable commands to the devices
> involved in the bridge configuration.  And it has done this for
> a _long_ time.  The ipv4 routing code will do the same.
> 
> This change is bogus and likely based upon behavior in some ancient
> distribution kernel that lacks the ethtool facilities.
> 
> I absolutely refuse to apply this.

Agreed. It is often devices that implement LRO, but don't have way
to turn it off.
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