On Wed, Oct 6, 2021 at 3:38 AM Ajit Khaparde <ajit.khapa...@broadcom.com> wrote: > > On Tue, Oct 5, 2021 at 10:31 AM Ferruh Yigit <ferruh.yi...@intel.com> wrote: > > > > There is a confusion on setting max Rx packet length, this patch aims to > > clarify it. > > > > 'rte_eth_dev_configure()' API accepts max Rx packet size via > > 'uint32_t max_rx_pkt_len' field of the config struct 'struct > > rte_eth_conf'. > > > > Also 'rte_eth_dev_set_mtu()' API can be used to set the MTU, and result > > stored into '(struct rte_eth_dev)->data->mtu'. > > > > These two APIs are related but they work in a disconnected way, they > > store the set values in different variables which makes hard to figure > > out which one to use, also having two different method for a related > > functionality is confusing for the users. > > > > Other issues causing confusion is: > > * maximum transmission unit (MTU) is payload of the Ethernet frame. And > > 'max_rx_pkt_len' is the size of the Ethernet frame. Difference is > > Ethernet frame overhead, and this overhead may be different from > > device to device based on what device supports, like VLAN and QinQ. > > * 'max_rx_pkt_len' is only valid when application requested jumbo frame, > > which adds additional confusion and some APIs and PMDs already > > discards this documented behavior. > > * For the jumbo frame enabled case, 'max_rx_pkt_len' is an mandatory > > field, this adds configuration complexity for application. > > > > As solution, both APIs gets MTU as parameter, and both saves the result > > in same variable '(struct rte_eth_dev)->data->mtu'. For this > > 'max_rx_pkt_len' updated as 'mtu', and it is always valid independent > > from jumbo frame. > > > > For 'rte_eth_dev_configure()', 'dev->data->dev_conf.rxmode.mtu' is user > > request and it should be used only within configure function and result > > should be stored to '(struct rte_eth_dev)->data->mtu'. After that point > > both application and PMD uses MTU from this variable. > > > > When application doesn't provide an MTU during 'rte_eth_dev_configure()' > > default 'RTE_ETHER_MTU' value is used. > > > > Additional clarification done on scattered Rx configuration, in > > relation to MTU and Rx buffer size. > > MTU is used to configure the device for physical Rx/Tx size limitation, > > Rx buffer is where to store Rx packets, many PMDs use mbuf data buffer > > size as Rx buffer size. > > PMDs compare MTU against Rx buffer size to decide enabling scattered Rx > > or not. If scattered Rx is not supported by device, MTU bigger than Rx > > buffer size should fail. > > > > Signed-off-by: Ferruh Yigit <ferruh.yi...@intel.com> > > --- > > Cc: Min Hu (Connor) <humi...@huawei.com> > > > > v2: > > * Converted to explicit checks for zero/non-zero > > * fixed hns3 checks > > * fixed some sample app rxmode.mtu value > > * fixed some sample app max-pkt-len argument and updated doc for it > > > > v3: > > * rebased > > > > v4: > > * fix typos in commit logs > > That's a lot of detail in the log. Thanks > > Acked-by: Ajit Khaparde <ajit.khapa...@broadcom.com>
Acked-by: Somnath Kotur <somnath.ko...@broadcom.com>
