netdev - Re: [Patch 2/2] mlx4: add dynamic LRO disable support

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Date:	Thu, 17 Jun 2010 18:54:28 +0800
From:	Cong Wang <amwang@...hat.com>
To:	Stanislaw Gruszka <sgruszka@...hat.com>
CC:	Ben Hutchings <bhutchings@...arflare.com>, netdev@...r.kernel.org,
	herbert.xu@...hat.com, nhorman@...hat.com, davem@...emloft.net
Subject: Re: [Patch 2/2] mlx4: add dynamic LRO disable support

On 06/15/10 17:39, Stanislaw Gruszka wrote:
> On Tue, 15 Jun 2010 16:53:27 +0800
> Cong Wang<amwang@...hat.com>  wrote:
>
>>> If so, it's better to stop device before modify LRO settings. I suggest
>>> something like that in mlx4_ethtool_op_set_flags:
>>>
>>> if (!!(data&   ETH_FLAG_LRO) != !!(dev->features&   NETIF_F_LRO)) {
>>
>> What does this line mean? This is to ignore all other flags, right?
>
> Yes, plus check if we are really changing current settings.
>
>>> 	/* Need to toggle LRO */
>>>
>>> 	if (netdev_running(dev)) {
>>>                  mutex_lock(&mdev->state_lock);
>>>                  mlx4_en_stop_port(dev);
>>>                  rc = mlx4_en_start_port(dev);
>>>                  if (rc)
>>>                          en_err(priv, "Failed to restart port\n");
>>> 	}
>>>
>>> 	dev->features ^= NETIF_F_LRO;
>>>
>>> 	if (netdev_running(dev))
>>>                  mutex_unlock(&mdev->state_lock);
>>> }
>>>
>>
>> I don't think mdev->state_lock is used to protect dev->feature.
>> rtnl_lock is. I think switching to mlx4_ethtool_op_set_flags()
>> from the default one has already solved this.
>
> Ahh, you have right, may intention was use it to stop and start
> port. Code rather should look like below:
>
> 	if (netdev_running(dev)) {
> 		mutex_lock(&mdev->state_lock);
> 		mlx4_en_stop_port(dev);
> 	}
>
> 	dev->features ^= NETIF_F_LRO;
>
> 	if (netdev_running(dev)) {
> 		rc = mlx4_en_start_port(dev);
> 		mutex_unlock(&mdev->state_lock);
>   		if (rc)
> 		en_err(priv, "Failed to restart port\n");
> 	}
>

Hmm, you mean ->features should be changed after port is stopped?
Why?
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