Subject: Re: [PATCH 1/2] igb: Allow extra 4 bytes on RX for vlan tags.

From: Ben Greear <[email-masked]>
Date: Thu, 17 Feb 2011 09:28:56 -0800

On 02/17/2011 03:04 AM, Jeff Kirsher wrote:
> On Thu, Feb 10, 2011 at 13:59,<[email-masked]>  wrote:
>> From: Ben Greear<[email-masked]>
>>
>> This allows the NIC to receive 1518 byte (not counting
>> FCS) packets when MTU is 1500, thus allowing 1500 MTU
>> VLAN frames to be received.  Please note that no VLANs
>> were actually configured on the NIC...it was just acting
>> as pass-through device.
>>
>> Signed-off-by: Ben Greear<[email-masked]>
>> ---
>> :100644 100644 58c665b... 30c9cc6... M  drivers/net/igb/igb_main.c
>>   drivers/net/igb/igb_main.c |    5 +++--
>>   1 files changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/net/igb/igb_main.c b/drivers/net/igb/igb_main.c
>> index 58c665b..30c9cc6 100644
>> --- a/drivers/net/igb/igb_main.c
>> +++ b/drivers/net/igb/igb_main.c
>> @@ -2281,7 +2281,8 @@ static int __devinit igb_sw_init(struct igb_adapter *adapter)
>>         adapter->rx_itr_setting = IGB_DEFAULT_ITR;
>>         adapter->tx_itr_setting = IGB_DEFAULT_ITR;
>>
>> -       adapter->max_frame_size = netdev->mtu + ETH_HLEN + ETH_FCS_LEN;
>> +       adapter->max_frame_size = (netdev->mtu + ETH_HLEN + ETH_FCS_LEN
>> +                                  + VLAN_HLEN);
>>         adapter->min_frame_size = ETH_ZLEN + ETH_FCS_LEN;
>>
>>         spin_lock_init(&adapter->stats64_lock);
>> @@ -4303,7 +4304,7 @@ static int igb_change_mtu(struct net_device *netdev, int new_mtu)
>>   {
>>         struct igb_adapter *adapter = netdev_priv(netdev);
>>         struct pci_dev *pdev = adapter->pdev;
>> -       int max_frame = new_mtu + ETH_HLEN + ETH_FCS_LEN;
>> +       int max_frame = new_mtu + ETH_HLEN + ETH_FCS_LEN + VLAN_HLEN;
>>         u32 rx_buffer_len, i;
>>
>>         if ((new_mtu<  68) || (max_frame>  MAX_JUMBO_FRAME_SIZE)) {
>
> While testing this patch, validation found that the patch reduces the
> maximum mtu size
> by 4 bytes (reduces it from 9216 to 9212).  This is not a desired side
> effect of this patch.

You could add handling for that case and have it act as it used to when
new_mtu is greater than 9212?

I tested e1000e and it worked w/out hacking at 1500 MTU, so maybe
check how it does it?

Thanks,
Ben

-- 
Ben Greear <[email-masked]>
Candela Technologies Inc  http://www.candelatech.com