<div data-ntes="ntes_mail_body_root" style="line-height:1.7;color:#000000;font-size:14px;font-family:Arial"><div style="margin:0;"><p style="white-space: normal; word-break: break-word !important; color: rgb(0, 0, 0); font-family: Arial; font-size: 14px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">Dear DPDK Development Team and Chelsio Support Team,<p style="white-space: normal; word-break: break-word !important; color: rgb(0, 0, 0); font-family: Arial; font-size: 14px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">We are writing to report two severe, fundamental issues we've encountered while using Chelsio T5/T6 series NICs (with the <code style="white-space: normal !important; word-break: break-word !important;">cxgbe</code> PMD) in our high-performance real-time audio streaming application. These problems prevent us from leveraging core DPDK features and require your urgent attention.<p style="white-space: normal; word-break: break-word !important; color: rgb(0, 0, 0); font-family: Arial; font-size: 14px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">Issue #1: Complete Failure to Transmit Zero-Copy (Multi-Segment) Packets<p style="white-space: normal; word-break: break-word !important; color: rgb(0, 0, 0); font-family: Arial; font-size: 14px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">To achieve the lowest latency, we are using the standard DPDK zero-copy mechanism: attaching an external shared memory buffer (from <code style="white-space: normal !important; word-break: break-word !important;">rte_memzone</code>) containing our audio payload to an mbuf header using <code style="white-space: normal !important; word-break: break-word !important;">rte_pktmbuf_attach_extbuf</code>. This correctly creates a multi-segment mbuf (<code style="white-space: normal !important; word-break: break-word !important;">nb_segs > 1</code>).<p style="white-space: normal; word-break: break-word !important; color: rgb(0, 0, 0); font-family: Arial; font-size: 14px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">However, we have found that the <code style="white-space: normal !important; word-break: break-word !important;">cxgbe</code> driver is completely unable to transmit these multi-segment mbufs. Any attempt to send such a packet via <code style="white-space: normal !important; word-break: break-word !important;">rte_eth_tx_burst</code> fails (returns 0 or results in silent packet drops), regardless of whether hardware offloads are enabled or disabled. The <code style="white-space: normal !important; word-break: break-word !important;">cxgbe</code> PMD's capability report (<code style="white-space: normal !important; word-break: break-word !important;">tx_offload_capa</code>) correctly does not include the <code style="white-space: normal !important; word-break: break-word !important;">RTE_ETH_TX_OFFLOAD_MULTI_SEGS</code> flag.<p style="white-space: normal; word-break: break-word !important; color: rgb(0, 0, 0); font-family: Arial; font-size: 14px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">This means that for the <code style="white-space: normal !important; word-break: break-word !important;">cxgbe</code> driver, the standard zero-copy path in DPDK is entirely non-functional.<p style="white-space: normal; word-break: break-word !important; color: rgb(0, 0, 0); font-family: Arial; font-size: 14px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">Issue #2: Incomplete Hardware Checksum Offload<p style="white-space: normal; word-break: break-word !important; color: rgb(0, 0, 0); font-family: Arial; font-size: 14px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">Forced to abandon zero-copy, we implemented a "single-copy" workaround by using <code style="white-space: normal !important; word-break: break-word !important;">rte_memcpy</code> to create a contiguous, single-segment mbuf. While this allows packets to be transmitted, we discovered a second critical issue: the hardware checksum offload functionality is incomplete.<p style="white-space: normal; word-break: break-word !important; color: rgb(0, 0, 0); font-family: Arial; font-size: 14px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">Specifically:<ol style="white-space: normal; word-break: break-word !important; color: rgb(0, 0, 0); font-family: Arial; font-size: 14px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;"><li style="white-space: normal !important; word-break: break-word !important;">We set the full offload flags on the mbuf: <code style="white-space: normal !important; word-break: break-word !important;">m->ol_flags |= RTE_MBUF_F_TX_IPV4 | RTE_MBUF_F_TX_IP_CKSUM | RTE_MBUF_F_TX_UDP_CKSUM;</code>.</li><li style="white-space: normal !important; word-break: break-word !important;">We zero out both the IP and UDP checksum fields in their respective headers before transmission.</li><li style="white-space: normal !important; word-break: break-word !important;">Packet captures reveal that only the UDP checksum is correctly calculated and filled in by the hardware. The IP checksum field remains zeroed, causing the packet to be treated as invalid and dropped by the network.</li><li style="white-space: normal !important; word-break: break-word !important;">For the packet to be transmitted successfully, we are forced to manually calculate the IP checksum in software (<code style="white-space: normal !important; word-break: break-word !important;">ip_h->hdr_checksum = rte_ipv4_cksum(ip_h);</code>) while keeping the UDP checksum field zeroed for hardware offload.</li></ol><p style="white-space: normal; word-break: break-word !important; color: rgb(0, 0, 0); font-family: Arial; font-size: 14px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">This proves that although the <code style="white-space: normal !important; word-break: break-word !important;">cxgbe</code> PMD reports support for <code style="white-space: normal !important; word-break: break-word !important;">RTE_ETH_TX_OFFLOAD_IPV4_CKSUM</code>, it does not actually perform IP checksum offloading in practice.<p style="white-space: normal; word-break: break-word !important; color: rgb(0, 0, 0); font-family: Arial; font-size: 14px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">For contrast, we must emphasize that both of the core functionalities we've described��zero-copy (multi-segment mbuf) transmission and full (IP+UDP) hardware checksum offloading��work perfectly on the same testbed when using NICs from Intel (igc/i40e) and onboard Realtek(RTL8125) controllers. This strongly suggests that the issues are specific to the Chelsio cxgbe PMD.<p style="white-space: normal; word-break: break-word !important; color: rgb(0, 0, 0); font-family: Arial; font-size: 14px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">Our Dilemma<p style="white-space: normal; word-break: break-word !important; color: rgb(0, 0, 0); font-family: Arial; font-size: 14px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">These two issues leave us in an untenable position:<ul style="white-space: normal; word-break: break-word !important; color: rgb(0, 0, 0); font-family: Arial; font-size: 14px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;"><li style="white-space: normal !important; word-break: break-word !important;">The ideal zero-copy path is completely broken, preventing us from realizing a primary performance benefit of DPDK.</li><li style="white-space: normal !important; word-break: break-word !important;">The fallback single-copy path is highly inefficient, as it not only incurs the CPU cost of a <code style="white-space: normal !important; word-break: break-word !important;">memcpy</code> but also requires the additional CPU overhead of software IP checksum calculation, largely defeating the purpose of hardware offloads.</li></ul><p style="white-space: normal; word-break: break-word !important; color: rgb(0, 0, 0); font-family: Arial; font-size: 14px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">Our Questions<p style="white-space: normal; word-break: break-word !important; color: rgb(0, 0, 0); font-family: Arial; font-size: 14px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">We urgently need your help to clarify the following:<ol style="white-space: normal; word-break: break-word !important; color: rgb(0, 0, 0); font-family: Arial; font-size: 14px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;"><ul style="white-space: normal !important; word-break: break-word !important;"><li style="white-space: normal !important; word-break: break-word !important;"></li><li>Is this behavior from the <code>cxgbe</code> PMD (offloading only UDP checksum) consistent with the design expectations for a PMD in DPDK?</li><li>Does the DPDK framework provide any debugging mechanisms to trace why an explicitly set offload flag (<code>RTE_MBUF_F_TX_IP_CKSUM</code>) would be ignored by a PMD without reporting an error?</li></ul></ol><span class="selected" style="white-space: normal; word-break: break-word !important; color: rgb(0, 0, 0); font-family: Arial; font-size: 14px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;"> Resolving these issues is critical to the success of our project. Any information or guidance you can provide would be greatly appreciated.Our Environment<ul style="white-space: normal !important; word-break: break-word !important;"><li style="white-space: normal !important; word-break: break-word !important;">DPDK Version: 25.07</li><li style="white-space: normal !important; word-break: break-word !important;">NIC Model: <code style="white-space: normal !important; word-break: break-word !important;">Chelsio T520-CR</code></li><li style="white-space: normal !important; word-break: break-word !important;">OS & Kernel: Tinycore64 16.0 kernel 6.6.63</li></ul>Thank you for your time and attention to this urgent matter. We look forward to your response.Best regards, �𾴵� DPDK ��ŶӺ� Chelsio ��֧��Ŷӣ���Ǻã���ڿ��һ��Ҫ�󼫸ߵ�ʵʱ��Ƶ��Ŀ��Ŀǰ��ʹ�� Chelsio T5/T6 ϵ��<code style="white-space: normal !important; word-break: break-word !important;">cxgbe</code> PMD��ʱ��صĵײ㹦��ϰ�� DPDK �ĺ��޷��ӡ��ǿ��ǵĽ��Ԯ����һ��㿽�� mbuf��ݰ��ȫ�޷��͡�Ϊ��ʵ��ӳ٣��ǲ�� DPDK ��׼��㿽��ƣ�ͨ�� <code style="white-space: normal !important; word-break: break-word !important;">rte_pktmbuf_attach_extbuf</code> ��ⲿ��ڴ棨<code style="white-space: normal !important; word-break: break-word !important;">rte_memzone</code>��е��Ƶ��ݸ��ӵ� mbuf ͷ��֮�󡣴˲��ᴴ��һ���� mbuf (<code style="white-space: normal !important; word-break: break-word !important;">nb_segs > 1</code>)��Ȼ��Ƿ�� <code style="white-space: normal !important; word-break: break-word !important;">cxgbe</code> ��ȫ�޷��ֶ�� mbuf��һ�� <code style="white-space: normal !important; word-break: break-word !important;">rte_eth_tx_burst</code> ��ʹ��ݰ��Ƿ��Ӳ��ж�أ��Ͷ��ʧ�ܣ��ֵΪ 0 ��¶��ݰ��޷��ϡ�<code style="white-space: normal !important; word-break: break-word !important;">cxgbe</code> PMD ��棨<code style="white-space: normal !important; word-break: break-word !important;">tx_offload_capa</code>��Ҳȷʵ�� <code style="white-space: normal !important; word-break: break-word !important;">RTE_ETH_TX_OFFLOAD_MULTI_SEGS</code> ��־���� <code style="white-space: normal !important; word-break: break-word !important;">cxgbe</code> ��ԣ�DPDK �ı�׼�㿽��ȫ��õġ���Ӳ��У��ж�ع��ܲ��Ϊ��ƹ��⣬��Ǳ��Ȳ��á��Э��ֶ� <code style="white-space: normal !important; word-break: break-word !important;">rte_memcpy</code> ��ݵ�һ��ġ��ĵ�� mbuf �С��Ȼ��ַ�ʽ��Գɹ��Ƿ��˵ڶ��⣺Ӳ��ж�ع��ǲ�ȱ������Ϊ��<ol style="white-space: normal !important; word-break: break-word !important;"><li style="white-space: normal !important; word-break: break-word !important;">��Ϊ mbuf ��ж�ر�־��<code style="white-space: normal !important; word-break: break-word !important;">m->ol_flags |= RTE_MBUF_F_TX_IPV4 | RTE_MBUF_F_TX_IP_CKSUM | RTE_MBUF_F_TX_UDP_CKSUM;</code>��</li><li style="white-space: normal !important; word-break: break-word !important;">�ڷ��ǰ��ǽ� IP �� UDP ͷ��е�У��ֶζ��㡣</li><li style="white-space: normal !important; word-break: break-word !important;">ץ��֣�ֻ�� UDP У����Ӳ��ȷ��㲢��ˡ�� IP У���ֶ��Ȼ�� 0��¸ð��б��Ϊ��Ч��ݰ��</li><li style="white-space: normal !important; word-break: break-word !important;">��Ǳ��ֶ�� IP У��ͣ�<code style="white-space: normal !important; word-break: break-word !important;">ip_h->hdr_checksum = rte_ipv4_cksum(ip_h);</code>��ͬʱ�� UDP У��Ϊ 0��ݰ��ȷ��Ͳ��ն��֤��</li></ol>��֤ʵ�� <code style="white-space: normal !important; word-break: break-word !important;">cxgbe</code> PMD ��Ȼ��֧�� <code style="white-space: normal !important; word-break: break-word !important;">RTE_ETH_TX_OFFLOAD_IPV4_CKSUM</code>��ʵ�ʹ����δִ�� IP У��͵�Ӳ��ж������Ϊ�Աȣ��Ҫǿ��ǣ��Ĺ��ܡ��㿽�� mbuf��ͺ��Ӳ��У��ж�أ�IP+UDP��ǵ�ͬһ��ƽ̨�ϣ�ʹ�� Intel (igc/i40e) �� Realtek (RTL8125) �İ��ʱ��ȫ��ʹ��ȷ�ţ��ض�� Chelsio cxgbe PMD �ġ���ǵ����ʹ��˾��<ul style="white-space: normal !important; word-break: break-word !important;"><li style="white-space: normal !important; word-break: break-word !important;">��㿽��·��ȫ��ͨ�� DPDK �ĺ��޷��֡�</li><li style="white-space: normal !important; word-break: break-word !important;">��Э�ĵ��·��Ч�ʵ���� <code style="white-space: normal !important; word-break: break-word !important;">memcpy</code> �� CPU ��е� IP У��͵��㿪��ʹ��Ӳ��ж�صļ�ֵ��ۿۡ�</li></ul>��ǵ��⡿��Ǽ��İ��⣺<ol style="white-space: normal !important; word-break: break-word !important;"><ul style="white-space: normal !important; word-break: break-word !important;"><li style="white-space: normal !important; word-break: break-word !important;"></li><li><code>cxgbe</code> ��Ϊ��ֻж�� UDP У��ͣ��Ƿ�� DPDK �� PMD ��Ԥ�ڣ�</li><li>DPDK ��Ƿ��е��Ի��ƣ��׷��Ϊ��һ��ȷ��õ�ж�ر�־��<code>RTE_MBUF_F_TX_IP_CKSUM</code>��ᱻ PMD ��Ҳ��κδ�</li></ul></ol> ��Щ��ǵ��Ŀ�ܷ�ɹ��Ҫ��κ��ܹ��ǰ��Ľ��Ϣ��ǽ��ʤ�м����ǵĻ��Ϣ��<ul style="white-space: normal !important; word-break: break-word !important;"><li style="white-space: normal !important; word-break: break-word !important;">DPDK �汾��25.07</li><li style="white-space: normal !important; word-break: break-word !important;">��ͺţ�<code style="white-space: normal !important; word-break: break-word !important;">Chelsio T520-CR</code></li><li style="white-space: normal !important; word-break: break-word !important;">��ϵͳ��ں˰汾��Tinycore64 16.0 kernel 6.6.63</li></ul>��л��ʱ��͹�ע��Ǽ��е��ڴ��Ļظ����£��� </div></div>