Subject: Re: [PATCH net v2 2/2] ixgbe: Enable setting RSS table to default values

From: Joe Damato <[email-masked]>
Date: Sun, 16 Apr 2023 21:58:48 -0700

On Sun, Apr 16, 2023 at 07:12:23PM +0000, Joe Damato wrote:
> ethtool uses `ETHTOOL_GRXRINGS` to compute how many queues are supported
> by RSS. The driver should return the smaller of either:
>   - The maximum number of RSS queues the device supports, OR
>   - The number of RX queues configured
> 
> Prior to this change, running `ethtool -X $iface default` fails if the
> number of queues configured is larger than the number supported by RSS,
> even though changing the queue count correctly resets the flowhash to
> use all supported queues.
> 
> Other drivers (for example, i40e) will succeed but the flow hash will
> reset to support the maximum number of queues supported by RSS, even if
> that amount is smaller than the configured amount.
> 
> Prior to this change:
> 
> $ sudo ethtool -L eth1 combined 20
> $ sudo ethtool -x eth1
> RX flow hash indirection table for eth1 with 20 RX ring(s):
>     0:      0     1     2     3     4     5     6     7
>     8:      8     9    10    11    12    13    14    15
>    16:      0     1     2     3     4     5     6     7
>    24:      8     9    10    11    12    13    14    15
>    32:      0     1     2     3     4     5     6     7
> ...
> 
> You can see that the flowhash was correctly set to use the maximum
> number of queues supported by the driver (16).
> 
> However, asking the NIC to reset to "default" fails:
> 
> $ sudo ethtool -X eth1 default
> Cannot set RX flow hash configuration: Invalid argument
> 
> After this change, the flowhash can be reset to default which will use
> all of the available RSS queues (16) or the configured queue count,
> whichever is smaller.
> 
> Starting with eth1 which has 10 queues and a flowhash distributing to
> all 10 queues:
> 
> $ sudo ethtool -x eth1
> RX flow hash indirection table for eth1 with 10 RX ring(s):
>     0:      0     1     2     3     4     5     6     7
>     8:      8     9     0     1     2     3     4     5
>    16:      6     7     8     9     0     1     2     3
> ...
> 
> Increasing the queue count to 48 resets the flowhash to distribute to 16
> queues, as it did before this patch:
> 
> $ sudo ethtool -L eth1 combined 48
> $ sudo ethtool -x eth1
> RX flow hash indirection table for eth1 with 16 RX ring(s):
>     0:      0     1     2     3     4     5     6     7
>     8:      8     9    10    11    12    13    14    15
>    16:      0     1     2     3     4     5     6     7
> ...
> 
> Due to the other bugfix in this series, the flowhash can be set to use
> queues 0-5:
> 
> $ sudo ethtool -X eth1 equal 5
> $ sudo ethtool -x eth1
> RX flow hash indirection table for eth1 with 16 RX ring(s):
>     0:      0     1     2     3     4     0     1     2
>     8:      3     4     0     1     2     3     4     0
>    16:      1     2     3     4     0     1     2     3
> ...
> 
> Due to this bugfix, the flowhash can be reset to default and use 16
> queues:
> 
> $ sudo ethtool -X eth1 default
> $ sudo ethtool -x eth1
> RX flow hash indirection table for eth1 with 16 RX ring(s):
>     0:      0     1     2     3     4     5     6     7
>     8:      8     9    10    11    12    13    14    15
>    16:      0     1     2     3     4     5     6     7
> ...

Fixes: 91cd94bfe4f0 ("ixgbe: add basic support for setting and getting nfc
controls")

> Signed-off-by: Joe Damato <[email-masked]>
> Reviewed-by: Sridhar Samudrala <[email-masked]>
> ---
>  .../net/ethernet/intel/ixgbe/ixgbe_ethtool.c  | 19 ++++++++++---------
>  1 file changed, 10 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c
> index 821dfd323fa9..0bbad4a5cc2f 100644
> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c
> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c
> @@ -2665,6 +2665,14 @@ static int ixgbe_get_rss_hash_opts(struct ixgbe_adapter *adapter,
>  	return 0;
>  }
>  
> +static int ixgbe_rss_indir_tbl_max(struct ixgbe_adapter *adapter)
> +{
> +	if (adapter->hw.mac.type < ixgbe_mac_X550)
> +		return 16;
> +	else
> +		return 64;
> +}
> +
>  static int ixgbe_get_rxnfc(struct net_device *dev, struct ethtool_rxnfc *cmd,
>  			   u32 *rule_locs)
>  {
> @@ -2673,7 +2681,8 @@ static int ixgbe_get_rxnfc(struct net_device *dev, struct ethtool_rxnfc *cmd,
>  
>  	switch (cmd->cmd) {
>  	case ETHTOOL_GRXRINGS:
> -		cmd->data = adapter->num_rx_queues;
> +		cmd->data = min_t(int, adapter->num_rx_queues,
> +				  ixgbe_rss_indir_tbl_max(adapter));
>  		ret = 0;
>  		break;
>  	case ETHTOOL_GRXCLSRLCNT:
> @@ -3075,14 +3084,6 @@ static int ixgbe_set_rxnfc(struct net_device *dev, struct ethtool_rxnfc *cmd)
>  	return ret;
>  }
>  
> -static int ixgbe_rss_indir_tbl_max(struct ixgbe_adapter *adapter)
> -{
> -	if (adapter->hw.mac.type < ixgbe_mac_X550)
> -		return 16;
> -	else
> -		return 64;
> -}
> -
>  static u32 ixgbe_get_rxfh_key_size(struct net_device *netdev)
>  {
>  	return IXGBE_RSS_KEY_SIZE;
> -- 
> 2.25.1
>