iRDMA流量控制总结 - 1

iRDMA流量控制总结

1.0 内容简介

This will introduce Ethernet flow control on Intel® Ethernet 800 Series Network Adapters with RDMA driver - iRDMA, with a focus on best practices for Linux RDMA traffic. 我们将介绍英特尔®以太网 800 系列网络适配器上的以太网流量控制与 RDMA 驱动程序 - iRDMA，重点介绍Linux RDMA 流量控制的实例。

It includes:包括如下基本内容

• Background on Ethernet flow control (FC) and Data Center Bridging (DCB). 以太网流量控制（Ethernet flow control  FC）和数据中心桥接（Data Center Bridging DCB）的背景
• Differences between Link-level Flow Control (LFC) and Priority Flow Control (PFC). 链路级流量控制（Link-level Flow Control  LFC）和带优先级的流量控制（Priority Flow Control  PFC）的区别
• Configuration steps for each type on 800 Series Linux hosts. 在 Linux 主机上对800 系列的每种类型进行配置的步骤
• Verification tips. 验证流量控制

1.1  QoS/Flow Control Limitations on the 800 Series 800 系列上的 QoS/流量控制限制

• Although the 800 Series hardware supports eight Traffic Classes (TCs), the maximum supported configuration is four TCs per port. Only one TC can have Priority Flow Control enabled per port. 虽然 800 系列硬件支持八个流量类别 (Traffic Classes TC)，但每个端口最多支持四个 TC。每个端口只能有一个 TC 启用带优先级的流量控制。

Number of Adapter Ports	Traffic Class Recommendation	RDMA
1, 2, or 4	Up to four TCs, with one of them enabled with PFC.	Supported
More than 4	No DCB Support	Not Supported

• In RoCEv2 mode, if no flow control is detected (either LFC or PFC), the driver automatically de-tunes. This is an intentional design to allow RoCEv2 to operate without flow control, but with lower performance. 在 RoCEv2 模式下，如果检测不到流量控制（LFC 或 PFC）规则，驱动程序会自动取消流量控制。这是一种有意的设计，允许 RoCEv2 在没有流量控制的情况下运行，但性能较低。
• When the 800 Series is in firmware Link Layer Discovery Protocol (LLDP) mode, only three application priorities are supported. Software LLDP supports 32. This refers to the LLDP APP TLV - see man lldptool-app for more info. 当 800 系列处于(Firmware)FW链路层发现协议 (LLDP) 状态时，只支持三种应用优先级。而软件 LLDP 支持 32 个。这指的是 LLDP APP TLV - 更多信息请参阅 man lldptool-app。
  
  
   

2.0   Background背景介绍

                                                                                                   

2.1 Ethernet Flow Control以太网流量控制

By design, Ethernet is an unreliable protocol with no guarantee that packets arrive at their destination correctly and in order. Instead, Ethernet relies on upper-layer protocols (such as TCP) or applications to provide reliable service and error correction. 根据设计，以太网是一种不可靠的协议，不能保证数据包正确无误地到达目的地。相反，以太网依赖于上层协议（如 TCP）或应用程序来提供可靠的服务和纠错。

The 802.3x standard introduced flow control to the Ethernet protoco