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charset="us-ascii" Content-Transfer-Encoding: quoted-printable X-Content-Filtered-By: Mailman/MimeDel 2.1.15 Subject: [dpdk-dev] Issue with MTU/max_rx_pkt_len handling by different NICs/PMD drivers X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 24 Oct 2017 12:25:51 -0000 Hi, While testing MTU configuration of physical ports using OVS-DPDK we have fo= und that Fortville and Niantic behaves differently for Tagged packets. Both= allows TX of packets with size up to programmed MTU value but in receive d= irection Fortville drops packets of size equal to configured MTU. Additiona= lly, Fortville does not report any error/drop counter if packets with size = more than configured MTU (max frame size) are received. In Niantic we can s= ee error counters getting incremented if packets of size more than MTU are = received. When ports are started, device attribute max_rx_pkt_len is set during devic= e/queue init by application (OVS in our case) and this max_rx_pkt_len is us= ed to program hardware register in device which in turn determines the maxi= mum size of packet/frame that it can receive. What we have found during testing is that Niantic could receive tagged/unta= gged packets of size equal to max_rx_pkt_len but Fortville could only recei= ve tagged packets (single tag) up to size <=3D (max_rx_pkt_len - 4). Datash= eet of Niantic mentions that device implicitly accounts for VLAN tag(s) in= addition to Maximum Frame size programmed which is not the case for Fortvi= lle. This causes issue with MTU settings and maximum frame size that NIC ca= n receive with tagged and untagged traffic. We have tested it with OVS-DPDK where it uses device attribute max_rx_pkt_l= en to set max frame size in accordance with the configured MTU size of port= . However, Ixgbe (Niantic) and i40e (Fortville) interpret it differently. I= looked at some other PMD drivers and different drivers interpret dev_conf.= rxmode.max_rx_pkt_len differently i.e. some adds one or two VLAN, few don't= include it and some use this field differently. It creates issue with MTU = while running same application on different NICs and PMD drivers need to be= fixed to have consistent behavior with MTU/Max Frame Size settings. Regards, Nitin Katiyar