Subject: Re: RFS seems to have incompatiblities with bridged vlans

From: John Fastabend <[email-masked]>
Date: Tue, 08 Jun 2010 18:08:43 -0700

Tim Gardner wrote:
> On 06/08/2010 05:00 PM, Tom Herbert wrote:
>> How about only checking against dev->num_rx_queues when that value is
>> greater than one.  Since bonding device is calling alloc_netdev, it is
>> not going to set the queue mapping, but dev->num_rx_queues will be one
>> in that case (this handles any intermediate driver that does do
>> multiple queues).
>>
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index 6f330ce..30ab66d 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -2270,7 +2270,7 @@ static int get_rps_cpu(struct net_device *dev,
>> struct sk_buff *skb,
>>                  u16 v16[2];
>>          } ports;
>>
>> -       if (skb_rx_queue_recorded(skb)) {
>> +       if (skb_rx_queue_recorded(skb)&&  dev->num_rx_queues>  1) {
>>                  u16 index = skb_get_rx_queue(skb);
>>                  if (unlikely(index>= dev->num_rx_queues)) {
>>                          if (net_ratelimit()) {
>>

Problem with this is it doesn't address mis-aligned num_rx_queues.  For example 
with the bonding driver defaulting to 16 queues now. We could end up with a base 
driver with 16+ queues and a bond with 16.  Then we have the same issue again.

  eth0  -------> bond / bridge ---------> vlan.id
(nbrxq=64)      (nbrxq=16)              (nbrxq=X)

>>
>> On Tue, Jun 8, 2010 at 7:18 AM, Eric Dumazet<[email-masked]>  wrote:
>>> Le lundi 07 juin 2010 à 15:30 -0700, John Fastabend a écrit :
>>>
>>>> There is always a possibility that the underlying device sets the
>>>> queue_mapping to be greater then num_cpus.  Also I suspect the same
>>>> issue exists with bonding devices.  Maybe something like the following
>>>> is worth while? compile tested only,
>>>>
>>>> [PATCH] 8021q: vlan reassigns dev without check queue_mapping
>>>>
>>>> recv path reassigns skb->dev without sanity checking the
>>>> queue_mapping field.  This can result in the queue_mapping
>>>> field being set incorrectly if the new dev supports less
>>>> queues then the underlying device.
>>>>
>>>> This patch just resets the queue_mapping to 0 which should
>>>> resolve this issue?  Any thoughts?
>>>>
>>>> The same issue could happen on bonding devices as well.
>>>>
>>>> Signed-off-by: John Fastabend<[email-masked]>
>>>> ---
>>>>
>>>>    net/8021q/vlan_core.c |    6 ++++++
>>>>    1 files changed, 6 insertions(+), 0 deletions(-)
>>>>
>>>> diff --git a/net/8021q/vlan_core.c b/net/8021q/vlan_core.c
>>>> index bd537fc..ad309f8 100644
>>>> --- a/net/8021q/vlan_core.c
>>>> +++ b/net/8021q/vlan_core.c
>>>> @@ -21,6 +21,9 @@ int __vlan_hwaccel_rx(struct sk_buff *skb, struct
>>>> vlan_group *grp,
>>>>        if (!skb->dev)
>>>>                goto drop;
>>>>
>>>> +     if (unlikely(skb->queue_mapping>= skb->dev->real_num_tx_queues))
>>>> +             skb_set_queue_mapping(skb, 0);
>>>> +
>>>>        return (polling ? netif_receive_skb(skb) : netif_rx(skb));
>>>>
>>>>    drop:
>>>> @@ -93,6 +96,9 @@ vlan_gro_common(struct napi_struct *napi, struct
>>>> vlan_group *grp,
>>>>        if (!skb->dev)
>>>>                goto drop;
>>>>
>>>> +     if (unlikely(skb->queue_mapping>= skb->dev->real_num_tx_queues))
>>>> +             skb_set_queue_mapping(skb, 0);
>>>> +
>>>>        for (p = napi->gro_list; p; p = p->next) {
>>>>                NAPI_GRO_CB(p)->same_flow =
>>>>                        p->dev == skb->dev&&  !compare_ether_header(
>>>> --
>>> Only a workaround, added in hot path in a otherwise 'good' driver
>>> (multiqueue enabled and ready)

Agreed thanks!

>>>
>>> eth0  ------->  bond / bridge --------->  vlan.id
>>> (nbtxq=8)      (ntxbq=1)        (nbtxq=X)
>>>
>>> X is capped to 1 because of bond/bridge, while bond has no "queue"
>>> (LLTX driver)
>>>
>>> Solutions :
>>>
>>> 1) queue_mapping could be silently tested in get_rps_cpu()...
>>>
>>> diff --git a/net/core/dev.c b/net/core/dev.c
>>> index 6f330ce..3a3f7f6 100644
>>> --- a/net/core/dev.c
>>> +++ b/net/core/dev.c
>>> @@ -2272,14 +2272,11 @@ static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
>>>
>>>         if (skb_rx_queue_recorded(skb)) {
>>>                 u16 index = skb_get_rx_queue(skb);
>>> -               if (unlikely(index>= dev->num_rx_queues)) {
>>> -                       if (net_ratelimit()) {
>>> -                               pr_warning("%s received packet on queue "
>>> -                                       "%u, but number of RX queues is %u\n",
>>> -                                       dev->name, index, dev->num_rx_queues);
>>> -                       }
>>> -                       goto done;
>>> -               }
>>> +               if (WARN_ONCE(index>= dev->num_rx_queues,
>>> +                               KERN_WARNING "%s received packet on queue %u, "
>>> +                               "but number of RX queues is %u\n",
>>> +                               dev->name, index, dev->num_rx_queues))
>>> +                       index %= dev->num_rx_queues;
>>>                 rxqueue = dev->_rx + index;
>>>         } else
>>>                 rxqueue = dev->_rx;
>>>
>>>

Looks good to me.

>>>
>>> 2) bond/bridge should setup more queues, just in case.
>>>    We probably need to be able to make things more dynamic,
>>>    (propagate nbtxq between layers) but not for 2.6.35
>>>
>>>

The bonding driver is already multiq per Andy Gospodarek's patch commit bb1d912, 
but unless the bond and bridge devices use the max num_rx_queues of there 
underlying devices this could still go wrong.

The bonding driver would possibly need to increase num_rx_queues and 
num_tx_queues when a device is enslaved or be set to some maximum at init for 
this to work right.

>>>
>>> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
>>> index 5e12462..ce813dd 100644
>>> --- a/drivers/net/bonding/bond_main.c
>>> +++ b/drivers/net/bonding/bond_main.c
>>> @@ -5012,8 +5012,8 @@ int bond_create(struct net *net, const char *name)
>>>
>>>         rtnl_lock();
>>>
>>> -       bond_dev = alloc_netdev(sizeof(struct bonding), name ? name : "",
>>> -                               bond_setup);
>>> +       bond_dev = alloc_netdev_mq(sizeof(struct bonding), name ? name : "",
>>> +                                  bond_setup, max(64, nr_cpu_ids));
>>>         if (!bond_dev) {
>>>                 pr_err("%s: eek! can't alloc netdev!\n", name);
>>>                 rtnl_unlock();
>>>
>>>
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> 
> Huh, so you guys are looking at the same issue (only my issue is RPS). 
> See http://marc.info/?l=linux-netdev&m=127603240621028&w=2. I'm in favor 
> of dropping the warning when no queues have been allocated.
> 
> How about this (see attached).

Prefer Eric's patch see first comment.

Thanks,
John

> rtg