Subject: Re: [v3 Patch 2/2] mlx4: add dynamic LRO disable support

From: Cong Wang <[email-masked]>
Date: Tue, 22 Jun 2010 16:42:04 +0800

On 06/21/10 17:02, Stanislaw Gruszka wrote:
> On Mon, Jun 21, 2010 at 10:23:00AM +0800, Cong Wang wrote:
>> On 06/18/10 19:09, Stanislaw Gruszka wrote:
>>> On Fri, Jun 18, 2010 at 06:55:38AM -0400, Amerigo Wang wrote:
>>>> +static int mlx4_ethtool_op_set_flags(struct net_device *dev, u32 data)
>>>> +{
>>>> +	struct mlx4_en_priv *priv = netdev_priv(dev);
>>>> +	struct mlx4_en_dev *mdev = priv->mdev;
>>>> +	int rc = 0;
>>>> +	int changed = 0;
>>>> +
>>>> +	if (data&   (ETH_FLAG_NTUPLE | ETH_FLAG_RXHASH))
>>>> +		return -EOPNOTSUPP;
>
> As we are here, better would be
> 	if (data&  ~ETH_FLAG_LRO)
> 		return -EOPNOTSUPP;
> code will persist correct when someone add new flags.

Yeah, better.

>
>>>> +
>>>> +	if (data&   ETH_FLAG_LRO) {
>>>> +		if (!(dev->features&   NETIF_F_LRO))
>>>> +			changed = 1;
>>>> +	} else if (dev->features&   NETIF_F_LRO) {
>>>> +		changed = 1;
>>>> +		mdev->profile.num_lro = 0;
>>>
>>> Everything fine except that, what for you zero num_lro value?
>>>
>>> If we set it to zero it will stay zero and we will not create
>>> proper number of lro descriptors in mlx4_en_create_rx_ring()
>>> (called from mlx4_en_set_ringparam() ->    mlx4_en_alloc_resources())
>>> when someone enable LRO again on.
>>>
>>
>> Huh? Isn't ->num_lro which controls LRO of mlx4 driver?
>
> It is, but only in mlx4_en_add() just before register_netdev(),
> when we setup default dev->features. Otherwise dev->features
> tells if LRO is enabled or disabled.
>
> This realize me, that we should not dev->features |= NETIF_F_LRO
> if mdev->profile.num_lro == 0 .
>

Got it! I misunderstood ->num_lro. :( Setting NETIF_F_LRO should be enough
for mlx4 driver...

I will send the updated version.

Thanks!