Subject: Re: [PATCH net-next 2/2] net/mlx4_en: Support for configurable RSS hash function

From: Or Gerlitz <[email-masked]>
Date: Wed, 5 Nov 2014 15:30:12 +0200

On 11/5/2014 3:05 PM, Eyal perry wrote:
> On 11/5/2014 2:27 PM, Or Gerlitz wrote:
>>> +
>>> +static int mlx4_en_set_rxfh_func(struct net_device *dev, u32 hfunc)
>>> +{
>>> +    struct mlx4_en_priv *priv = netdev_priv(dev);
>>> +    struct mlx4_en_dev *mdev = priv->mdev;
>>> +    u32 prev_rss_hash_fn = priv->rss_hash_fn;
>>> +    int err = 0;
>>> +
>>> +    if (!(hfunc & priv->rss_hash_fn_caps))
>>> +        return -EINVAL;
>>> +
>>> +    priv->rss_hash_fn = hfunc;
>> Seems that you are blindly setting here priv->rss_hash_fn to the function (xor or top) requested by the user w.o prior checking if the firmware actually supports that
>> (e.g test it against priv->rss_hash_fn_caps, right?
>>
> That exactly what I do 3 lines above, priv->rss_hash_fn_caps is derived from firmware capabilities.

got it, thanks.

>
> [...]
>
>>> --- a/drivers/net/ethernet/mellanox/mlx4/en_rx.c
>>> +++ b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
>>> @@ -1113,10 +1113,13 @@ int mlx4_en_config_rss_steer(struct
>>> mlx4_en_priv *priv)
>>>        }
>>>          rss_context->flags = rss_mask;
>>> -    rss_context->hash_fn = MLX4_RSS_HASH_TOP;
>>> -    for (i = 0; i < 10; i++)
>>> -        rss_context->rss_key[i] = cpu_to_be32(rsskey[i]);
>>> -
>>> +    if (priv->rss_hash_fn & MLX4_RSS_HASH_XOR) {
>>> +        rss_context->hash_fn = MLX4_RSS_HASH_XOR;
>>> +    } else {
>>> +        rss_context->hash_fn = MLX4_RSS_HASH_TOP;
>>> +        for (i = 0; i < 10; i++)
>>> +            rss_context->rss_key[i] = cpu_to_be32(rsskey[i]);
>>> +    }
>> So this patch effectively changes the default from top to xor, right? is
>> that intentional? if yes, spare few words on the change log.
>>
> No, in general the default shouldn't be affected by the patch (unless
> there's a bug). The default value is set in mlx4_en_init_netdev() and it
> will remain Toeplitz unless firmware is supports only XOR hash function.
>

Oh, I see why I was confused and what I think need to be fixed. You are 
using both MLX4_RSS_HASH_TOP/XOR and RSS_HASH_TOP/XOR, any reason for that?

Also, priv->rss_hash_fn should equal one value, right? so this code "if 
(priv->rss_hash_fn & something)" is confusing, should be "if 
(priv->rss_hash_fn == something)"

Or.