netdev - Re: RFS seems to have incompatiblities with bridged vlans

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Date:	Mon, 07 Jun 2010 15:30:42 -0700
From:	John Fastabend <john.r.fastabend@...el.com>
To:	Stephen Hemminger <shemminger@...tta.com>
CC:	Peter Lieven <pl@....net>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: RFS seems to have incompatiblities with bridged vlans

Stephen Hemminger wrote:
> On Mon, 7 Jun 2010 22:36:11 +0200
> Peter Lieven <pl@....net> wrote:
> 
>> Hi,
>>
>> i today tried out 2.6.32-rc2 and I see a lot of warning messages like this:
>>
>> Jun  7 22:33:15 172.21.55.20 kernel: [ 3012.575884] br141 received packet on queue 4, but number of RX queues is 1
>>
>> The host is a SMP system with 8 cores, so I think there is expected to be one rx queue per CPU, but it seems
>> the bridge iface has only one.
>>
> 
> The bridge interface has no queues. It doesn't queue any packets. 
> The test in receive packet path is not appropriate in this case.
> Not sure what the right fix is. Pretending the bridge device has
> multiple queues (num_queues == NUM_CPUS) is a possibility but
> seems like overhead without real increase in parallelism.
> 
> 
> 

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 <john.r.fastabend@...el.com>
---

  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(
--
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