netdev - Re: [PATCH 07/10] net: remove NETIF_F_NO

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Message-ID: <20110714205623.GD16759@rere.qmqm.pl>
Date:	Thu, 14 Jul 2011 22:56:23 +0200
From:	Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:	Tom Herbert <therbert@...gle.com>
Cc:	Ben Hutchings <bhutchings@...arflare.com>, netdev@...r.kernel.org
Subject: Re: [PATCH 07/10] net: remove NETIF_F_NO_CSUM feature

On Wed, Jul 13, 2011 at 05:30:37PM -0700, Tom Herbert wrote:
> On Wed, Jul 13, 2011 at 5:23 PM, Ben Hutchings <bhutchings@...arflare.com>wrote:
> > On Thu, 2011-07-14 at 02:10 +0200, Michał Mirosław wrote:
> > > There are no explicit users, so this is now equivalent to
> > NETIF_F_HW_CSUM.
> > [...]
> > I think this is still a useful distinction, even the networking core
> > currently doesn't care about the difference.
> Agreed.  It seems like this is the only way to distinguish virtual devices
> from HW devices (like we did with nocachecopy check).

You can't reliably detect virtual devices by this method. No tunnel devices
use this flag and it also doesn't detect e.g. IPsec being used on the route
(and no-cache copy should be disabled at least for software encryption).

That's why its turned off by default and should be enabled only when user
knows he will win some pps with it.

Best Regards,
Michał Mirosław
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