[v4,net-next] MPLS: Use mpls_features to activate software MPLS GSO segmentation

Hi Eric,

On Mon, Jun 02, 2014 at 08:42:02PM -0700, Eric Dumazet wrote:
> Hi Simon
> 
> On Tue, 2014-06-03 at 11:38 +0900, Simon Horman wrote:
> > +/* If MPLS offload request, verify we are testing hardware MPLS features
> > + * instead of standard features for the netdev.
> > + */
> > +#ifdef CONFIG_NET_MPLS_GSO
> > +static netdev_features_t net_mpls_features(struct sk_buff *skb,
> > +					   netdev_features_t features)
> > +{
> > +	int tmp;
> > +	__be16 type;
> > +
> > +	type = skb_network_protocol(skb, &tmp);
> > +	if (unlikely(type == cpu_to_be16(ETH_P_MPLS_UC) ||
> > +		     type == cpu_to_be16(ETH_P_MPLS_MC)))
> 
> I believe net/core/dev.c prefers to use htons(ETH_P_MPLS_UC)

Thanks, I will fix that.

> (check netif_skb_features())
> 
> > +		features &= skb->dev->mpls_features;
> > +
> > +	return features;
> > +}
> > +#else
> > +static netdev_features_t net_mpls_features(struct sk_buff *skb,
> > +					   netdev_features_t features)
> > +{
> > +	return features;
> > +}
> > +#endif
> > +
> >  static netdev_features_t harmonize_features(struct sk_buff *skb,
> >  	netdev_features_t features)
> >  {
> >  	int tmp;
> 
> 	_be16 type;
> 
> 	type = skb_network_protocol(skb, &tmp);
> 
> >  
> > +	features = net_mpls_features(skb, features);
> 
> 	features = net_mpls_features(skb, features, type);
> 
> > +
> >  	if (skb->ip_summed != CHECKSUM_NONE &&
> >  	    !can_checksum_protocol(features, skb_network_protocol(skb, &tmp))) {
> 
> 	!can_checksum_protocol(features, type)) {
> 
> >  		features &= ~NETIF_F_ALL_CSUM;

Thanks, I'll switch things around as you suggest.

> I guess CONFIG_NET_MPLS_GSO will be set by all distros, right ?

That seems likely to me.


From: Simon Horman <horms@verge.net.au>

MPLS: Use mpls_features to activate software MPLS GSO segmentation

If an MPLS packet requires segmentation then use mpls_features
to determine if the software implementation should be used.

As no driver advertises MPLS GSO segmentation this will always be
the case.

I had not noticed that this was necessary before as software MPLS GSO
segmentation was already being used in my test environment. I believe that
the reason for that is the skbs in question always had fragments and the
driver I used does not advertise NETIF_F_FRAGLIST (which seems to be the
case for most drivers). Thus software segmentation was activated by
skb_gso_ok().

This introduces the overhead of an extra call to skb_network_protocol()
in the case where where CONFIG_NET_MPLS_GSO is set and
skb->ip_summed == CHECKSUM_NONE.

Thanks to Jesse Gross for prompting me to investigate this.

Signed-off-by: Simon Horman <horms@verge.net.au>

---
v4.2
* As suggested by Eric Dumazet
  - Use htons() instead of cpu_to_be16()
  - Refactor code to pass type to net_mpls_features.

v4.1
* Following fedback from Thomas Graff and Jesse Gross
  - Use ethertype of packet to detect MPLS rather than
    relying on mac_len indicating a gap between the end of L2
    and the beginning of L3. That assumption seems to
    be broken by the GRE GSO code.
  - Move mpls_features handling into harmonize_features()
    This allows an existing call in there to skb_network_protocol()
    to be leveraged.
  - Removed acks as the patch has now changed in a material way

v4
* As suggested by YAMAMOTO Takashi
  - Correct typos in comment
* Added Ack from YAMAMOTO Takashi
v3
* As requested by David Miller
  - Do not mark net_mpls_features as inline
  - Correct alignment of parameters

v2
* Added Ack from Jesse Gross
* Removed duplicate 'Thus' from changelog
---
 net/core/dev.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

> diff --git a/net/core/dev.c b/net/core/dev.c
> index 0355ca5..7c063ac 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -2498,13 +2498,42 @@ static int dev_gso_segment(struct sk_buff *skb, netdev_features_t features)
>  	return 0;
>  }
>  
> +/* If MPLS offload request, verify we are testing hardware MPLS features
> + * instead of standard features for the netdev.
> + */
> +#ifdef CONFIG_NET_MPLS_GSO
> +static netdev_features_t net_mpls_features(struct sk_buff *skb,
> +					   netdev_features_t features,
> +					   __be16 type)
> +{
> +	int tmp;

this variable seems no longer used.

> +
> +	if (unlikely(type == htons(ETH_P_MPLS_UC) ||
> +		     type == htons(ETH_P_MPLS_MC)))

why unlikely?

otherwise,
Acked-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>

YAMAMOTO Takashi
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On Tue, Jun 03, 2014 at 01:46:11PM +0900, YAMAMOTO Takashi wrote:
> > diff --git a/net/core/dev.c b/net/core/dev.c
> > index 0355ca5..7c063ac 100644
> > --- a/net/core/dev.c
> > +++ b/net/core/dev.c
> > @@ -2498,13 +2498,42 @@ static int dev_gso_segment(struct sk_buff *skb, netdev_features_t features)
> >  	return 0;
> >  }
> >  
> > +/* If MPLS offload request, verify we are testing hardware MPLS features
> > + * instead of standard features for the netdev.
> > + */
> > +#ifdef CONFIG_NET_MPLS_GSO
> > +static netdev_features_t net_mpls_features(struct sk_buff *skb,
> > +					   netdev_features_t features,
> > +					   __be16 type)
> > +{
> > +	int tmp;
> 
> this variable seems no longer used.

Thanks, I will remove it.

> > +
> > +	if (unlikely(type == htons(ETH_P_MPLS_UC) ||
> > +		     type == htons(ETH_P_MPLS_MC)))
> 
> why unlikely?

Because packets are not likely to be MPLS (IMHO).
I'm happy to remove the unlikely() if you like.

> 
> otherwise,
> Acked-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
> 
> YAMAMOTO Takashi
> 
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