netdev - Re: tap/bridge: Dropping NETIF_F_GSO/NETIF_F

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Date:	Thu, 5 May 2011 08:34:15 +1000
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Michał Mirosław <mirq-linux@...e.qmqm.pl>,
	netdev@...r.kernel.org, Ben Hutchings <bhutchings@...arflare.com>
Subject: Re: tap/bridge: Dropping NETIF_F_GSO/NETIF_F_SG

On Wed, May 04, 2011 at 09:18:14PM +0300, Michael S. Tsirkin wrote:
> BTW, I just noticed that net-next spits out
> many of the following when I run any VMs:
> 
> tap0: Dropping NETIF_F_SG since no checksum feature.
> tap0: Dropping NETIF_F_GSO since no SG feature.
> tap0: Features changed: 0x401b4849 -> 0x40004040
> device msttap0 entered promiscuous mode
> br0: Dropping NETIF_F_GSO since no SG feature.
> br0: port 1(msttap0) entering forwarding state
> br0: port 1(msttap0) entering forwarding state
> tap0: Features changed: 0x40004040 -> 0x40024849
> tap0: Dropping NETIF_F_SG since no checksum feature.
> tap0: Dropping NETIF_F_GSO since no SG feature.
> tap0: Features changed: 0x40024849 -> 0x40004040
> br0: Dropping NETIF_F_GSO since no SG feature.
> tap0: Dropping NETIF_F_SG since no checksum feature.
> tap0: Dropping NETIF_F_GSO since no SG feature.
> tap0: Dropping NETIF_F_SG since no checksum feature.
> tap0: Dropping NETIF_F_GSO since no SG feature.
> tap0: Dropping NETIF_F_SG since no checksum feature.
> tap0: Dropping NETIF_F_GSO since no SG feature.
> tap0: Dropping NETIF_F_SG since no checksum feature.
> tap0: Dropping NETIF_F_GSO since no SG feature.
> tap0: Features changed: 0x40004040 -> 0x401b4849
> tap0: Dropping NETIF_F_SG since no checksum feature.
> tap0: Dropping NETIF_F_GSO since no SG feature.
> tap0: Features changed: 0x401b4849 -> 0x40004040
> br0: Dropping NETIF_F_GSO since no SG feature.
> 
> My problem is not primarily with warnings:
> 
> will that linearize all packets and disable GSO
> for tap and bridge? If yes it can't be good
> for performance...

I think so.  So the question is why is checksum off?

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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