Re: [dpdk-dev] [PATCH v1 2/6] net/i40e: set min and max MTU for i40e devices

[Ian Stokes <ian.stokes@intel.com>]

On 3/19/2019 4:18 PM, Ferruh Yigit wrote:
> On 2/27/2019 9:45 PM, Ian Stokes wrote:
>> This commit sets the min and max supported MTU values for i40e devices
>> via the i40e_dev_info_get() function. Min MTU supported is set to
>> ETHER_MIN_MTU and max mtu is calculated as the max packet length
>> supported minus the transport overhead.
>>
>> Signed-off-by: Ian Stokes <ian.stokes@intel.com>
>> ---
>>   drivers/net/i40e/i40e_ethdev.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/net/i40e/i40e_ethdev.c b/drivers/net/i40e/i40e_ethdev.c
>> index dca61f03a..caab1624f 100644
>> --- a/drivers/net/i40e/i40e_ethdev.c
>> +++ b/drivers/net/i40e/i40e_ethdev.c
>> @@ -3499,6 +3499,8 @@ i40e_dev_info_get(struct rte_eth_dev *dev, struct rte_eth_dev_info *dev_info)
>>   	dev_info->max_rx_pktlen = I40E_FRAME_SIZE_MAX;
>>   	dev_info->max_mac_addrs = vsi->max_macaddrs;
>>   	dev_info->max_vfs = pci_dev->max_vfs;
>> +	dev_info->max_mtu = dev_info->max_rx_pktlen - I40E_ETH_OVERHEAD;
> 
> 'I40E_ETH_OVERHEAD' [1] is the max overhead, when VLAN and QINQ is not
> configured, we are wasting 8 bytes, should we try to be more fine grained when
> setting the max_mtu? Does it worth the complexity?
> 

I'm not against this, but for this patchset I was keeping the values to 
what have existed already.

There was discussion WRT being more dynamic and whether that was the 
responsibility of the application or DPDK.

http://mails.dpdk.org/archives/dev/2019-February/124457.html

I'm open to this changing in the future, but for the moment was happy to 
see it stay as it is until a resolution is agreed upon.

Ian
> 
> [1]
> (ETHER_HDR_LEN + ETHER_CRC_LEN + I40E_VLAN_TAG_SIZE * 2)
> 
>> +	dev_info->min_mtu = ETHER_MIN_MTU;
>>   	dev_info->rx_queue_offload_capa = 0;
>>   	dev_info->rx_offload_capa =
>>   		DEV_RX_OFFLOAD_VLAN_STRIP |
>>
>