摘要：DL_Active 跳变到 DL_Inactive（即从Physical LinkUp = 1b跳变到Physical LinkUp = 0b）。Surprise Down Error的定义强调了操作系统不知情，因此操作系统能感知的且会导致链路状态从link

什么是PCIe Surprise Down Error

PCIe Surprise Down Error 指的是在操作系统不知情的情况PCIe（Downstream Ports）设备下的物理层链路状态从

DL_Active 跳变到 DL_Inactive（即从Physical LinkUp = 1b跳变到Physical LinkUp = 0b）。Surprise Down Error的定义强调了操作系统不知情，因此操作系统能感知的且会导致链路状态从link up跳变到link down的事件则不会被当做Surprise Down Error处理。

Surprise Down Error记录在哪里

linux系统中在terminal中通过dmesg命令可以获取是否发生过Surprise Down Error相关的报错。

需要注意的是，dmesg显示的是曾经发生过的错误，即使目前环境因为重启或其他原因错误已经不存在了。

图1 ：dmesg报错

通过lspci -s $target_dsp -vvv 命令查看downstream port的Advanced Error Reporting能力结构中的Uncorrectable Error Status Register也可以查看当前是否存在Surprise Down Error。

需要注意的是，Surprise Down Error是记录在downstream port的上，表示downstream port与对接的upstream port设备的链路异常。lspci显示的当前环境中的实时状态，如果曾经发生过错误，但是因为downstream port对接的设备已经发生过重启，错误状态会被清除。

Uncorrectable Error Status Register的Surprise Down Error Status字段（bit 5）为1表示存在Surprise Down Error(缩写为SDES)。

出现Surprise Down Error的场景

导致Surprise Down Error的常见场景如下：

硬件故障： PCIe 接口卡接触不良且不小心触碰导致物理层link down。

电源问题：设备供电异常，如电压波动、突然断电等，可能使设备意外下电，产生 Surprise Down Error。

热插拔事件：未按照标准的热插拔流程进行操作，例如在不支持暴力拔出的设备上直接拔出 PCIe 设备，会导致操作系统无法及时感知设备的移除，进而触发Surprise Down Error

意外重启：PCIe设备（例如智能网卡）在某些异常场景下会主动重启从而导致 Surprise Down Error。

当智能网卡内嵌CPU因为异常而无法响应某些进程时，此时可能会主动触发网卡芯片复位，从而解决异常。

注意事项：

PCIe协议详细描述了如下hot reset、link disable、功耗管理、热插拔等事件不会被当做Surprise Down Error处理

• If the Secondary Bus Reset bit in the Bridge Control register has been Set by software, then the subsequent transition to DL_Inactive must not be considered an error.

• If the Link Disable bit has been Set by software, then the subsequent transition to DL_Inactive must not be considered an error.

• If a Switch Downstream Port transitions to DL_Inactive due to an event above that Port, that transition to DL_Inactive must not be considered an error. Example events include the Switch Upstream Port propagating

Hot Reset, the Switch Upstream Link transitioning to DL_Down, and the Secondary Bus Reset bit in the Switch Upstream Port being Set.

• If a PME_Turn_Off Message has been sent through this Port, then the subsequent transition to DL_Inactive must not be considered an error.

• Note that the DL_Inactive transition for this condition will not occur until a power off, a reset, or a request to restore the Link is sent to the Physical Layer.

• Note also that in the case where the PME_Turn_Off/PME_TO_Ack handshake fails to complete successfully, a Surprise Down error may be detected.

• If the Port is associated with a hot-pluggable slot (the Hot-Plug Capable bit in the Slot Capabilities register Set), and the Hot-Plug Surprise bit in the Slot Capabilities register is Set, then any transition to DL_Inactive

must not be considered an error.

• If the Port is associated with a hot-pluggable slot (Hot-Plug Capable bit in the Slot Capabilities register Set), and Power Controller Control bit in Slot Control register is Set (Power-Off), then any transition to DL_Inactive must not be considered an error.

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来源：新浪财经