> -----Original Message----- > From: Ferruh Yigit <ferruh.yi...@intel.com> > Sent: Tuesday, October 12, 2021 8:54 AM [...] > Subject: [PATCH v6 1/6] ethdev: fix max Rx packet length > > 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> > Acked-by: Ajit Khaparde <ajit.khapa...@broadcom.com> > Acked-by: Somnath Kotur <somnath.ko...@broadcom.com> > Acked-by: Huisong Li <lihuis...@huawei.com> > ---
For net/enic, Acked-by: Hyong Youb Kim <hyon...@cisco.com> Thanks. -Hyong
