RE: [Xen-users] Ethernet MTU

["Dmitri Bichko" <dbichko@xxxxxxxxxxxxxx>]

Any chance this made it into 3.0.3?

It'd be really nice to be able to set MTU 9000 for some free performance
improvements for iSCSI.

Thanks,
Dmitri

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> Daniele Palumbo
> Sent: Wednesday, September 13, 2006 10:55 AM
> To: xen-users@xxxxxxxxxxxxxxxxxxx
> Cc: xen-devel
> Subject: Re: [Xen-users] Ethernet MTU
> 
> 
> I have some news...
> 
> On Wednesday 16 August 2006 22:53, Dominique Rousseau wrote:
> > After some tries, it looks like the vif code don't handle 
> frames with 
> > size larger than 1500.
> 
> true: 
> http://lists.xensource.com/archives/html/xen-devel/2006-08/msg
> 00944.html
> 
> > Looking at the code, there is the following snippet that 
> seems to be 
> > the probleme (in drivers/xen/netback/netback.c) :
> >
> >                if (unlikely(txreq.size < ETH_HLEN) ||
> >                    unlikely(txreq.size > ETH_FRAME_LEN)) {
> >                        DPRINTK("Bad packet size: %d\n", txreq.size);
> >                        make_tx_response(netif, txreq.id, 
> NETIF_RSP_ERROR);
> >                        netif_put(netif);
> >                        continue;
> >                }
> 
> ./include/linux/if_vlan.h:#define VLAN_ETH_FRAME_LEN    1518  
>   /* Max. octets 
> in frame sans FCS */
> ./include/linux/if_ether.h:#define ETH_FRAME_LEN        1514  
>           /* 
> Max. octets in frame sans FCS */
> 
> ./include/linux/if_vlan.h:#define VLAN_ETH_HLEN 18            
>   /* Total 
> octets in header.       */
> ./include/linux/if_ether.h:#define ETH_HLEN     14            
>   /* Total 
> octets in header.       */
> 
> netfront_vlan.patch:
> ---
> # Node ID a5ee1cb525bbe8954dc3332ceec951e09a378b68
> # parent: c097485037f7417b77db34da198b62a9c9481dc5
> Make MTU rx check in netfront more permissive to allow for 
> 8021q vlan tagging.
> 
> Signed-off-by: Keir Fraser <keir@xxxxxxxxxxxxx>
> 
> --- a/linux-2.6-xen-sparse/drivers/xen/netfront/netfront.c    
>   Wed Mar 15 
> 12:41:58 2006 +0100
> +++ b/linux-2.6-xen-sparse/drivers/xen/netfront/netfront.c    
>   Wed Mar 15 
> 12:52:33 2006 +0100
> @@ -845,11 +845,11 @@ static int netif_poll(struct net_device
>         }
> 
>         while ((skb = __skb_dequeue(&rxq)) != NULL) {
> -               if (skb->len > (dev->mtu + ETH_HLEN)) {
> +               if (skb->len > (dev->mtu + ETH_HLEN + 4)) {
>                         if (net_ratelimit())
>                                 printk(KERN_INFO "Received 
> packet too big 
> for "
>                                        "MTU (%d > %d)\n",
> -                                      skb->len - ETH_HLEN, dev->mtu);
> +                                      skb->len - ETH_HLEN - 4, 
> + dev->mtu);
>                         skb->len  = 0;
>                         skb->tail = skb->data;
>                         init_skb_shinfo(skb);
> ---
> 
> looking at all that things, maybe the solutions is to change 
> ETH_FRAME_LEN in 
> VLAN_ETH_FRAME_LEN...
> or to remove that check (already done in unstable).
> 
> i'll try tomorrow.
> 
> bye
> d.
> 
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> 


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