netdev - Re: [Lxc-users] Bad checksums and lost packets with macvlan on dummy

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Date:	Sun, 27 Feb 2011 20:50:36 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Daniel Lezcano <daniel.lezcano@...e.fr>
Cc:	Andrian Nord <nightnord@...il.com>,
	lxc-users@...ts.sourceforge.net, Patrick McHardy <kaber@...sh.net>,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: [Lxc-users] Bad checksums and lost packets with macvlan on
 dummy

Le dimanche 27 février 2011 à 16:14 +0100, Daniel Lezcano a écrit :
> On 02/23/2011 06:13 PM, Andrian Nord wrote:
> > On Mon, Feb 21, 2011 at 05:07:31PM +0100, Daniel Lezcano wrote:
> >> I Cc'ed the netdev mailing list and Patrick in case my analysis is wrong
> >> or incomplete.
> > I'm confirming, that this happens only when macvlan's are onto dummy net
> > device. In case of some physical interface under macvlan there is no lost
> > packages and no broken checksums.
> 
> I did some tests with a 2.6.35 kernel version and it seems the checksum 
> errors do not appear.
> I noticed there are some changes in the dummy setup function:
> 
>    dev->features   |= NETIF_F_SG | NETIF_F_FRAGLIST | NETIF_F_TSO;
>    dev->features   |= NETIF_F_NO_CSUM | NETIF_F_HIGHDMA | NETIF_F_LLTX;
> 
> 
> May be that was introduced by commit:
> 
> commit 6d81f41c58c69ddde497e9e640ba5805aa26e78c
> Author: Eric Dumazet <eric.dumazet@...il.com>
> Date:   Mon Sep 27 20:50:33 2010 +0000
> 
>      dummy: percpu stats and lockless xmit
> 
>      Converts dummy network device driver to :
> 
>      - percpu stats
> 
>      - 64bit stats
> 
>      - lockless xmit (NETIF_F_LLTX)
> 
>      - performance features added (NETIF_F_SG | NETIF_F_FRAGLIST |
>      NETIF_F_TSO | NETIF_F_NO_CSUM | NETIF_F_HIGHDMA)
> 
>      Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
>      Signed-off-by: David S. Miller <davem@...emloft.net>
> 
> 
> Eric,
> 
> Andrian is observing, with a couple of macvlan (in bridge mode) on top 
> of a dummy interface, a lot of checksums error and packets drop.
> Each macvlan is in a different network namespace and the dummy interface 
> is in the init_net.
> 
> Any ideas ?

Not sure I understand... I thought dummy was dropping all frames
anyway ?

static netdev_tx_t dummy_xmit(struct sk_buff *skb, struct net_device *dev)
{
        struct pcpu_dstats *dstats = this_cpu_ptr(dev->dstats);

        u64_stats_update_begin(&dstats->syncp);
        dstats->tx_packets++;
        dstats->tx_bytes += skb->len;
        u64_stats_update_end(&dstats->syncp);

        dev_kfree_skb(skb);
        return NETDEV_TX_OK;
}


Maybe you could describe the setup ?


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