虚拟 CPU 热插拔

以下是使用 QMP device_add 和 device_del 热插入、热移除 vCPU 的完整示例。

vCPU 热插入

1. 启动 QEMU，maxcpus 必须指定，才能热插入:

   $ qemu-system-x86_64 -display none -no-user-config -m 2048 \
       -nodefaults -monitor stdio -machine pc,accel=kvm,usb=off \
       -smp 1,maxcpus=2 -cpu IvyBridge-IBRS \
       -qmp unix:/tmp/qmp-sock,server=on,wait=off
   

2. 用源码树 scripts/qmp/ 中的 qmp-shell 连接刚启动的 QEMU:

   $> ./qmp-shell -p -v /tmp/qmp-sock
   [...]
   (QEMU)
   

3. 查询哪些 CPU 类型可以插入，以及可用插槽:

   (QEMU) query-hotpluggable-cpus
   {
       "execute": "query-hotpluggable-cpus",
       "arguments": {}
   }
   {
       "return": [
           {
               "props": {
                   "core-id": 1,
                   "socket-id": 0,
                   "thread-id": 0
               },
               "type": "IvyBridge-IBRS-x86_64-cpu",
               "vcpus-count": 1
           },
           {
               "props": {
                   "core-id": 0,
                   "socket-id": 0,
                   "thread-id": 0
               },
               "qom-path": "/machine/unattached/device[0]",
               "type": "IvyBridge-IBRS-x86_64-cpu",
               "vcpus-count": 1
           }
       ]
   }
   (QEMU)
   

4. 返回对象中，有 qom-path 的 CPU 已存在，没有的可热插入。上例显示 插槽 0、核心 0 已有 IvyBridge-IBRS-x86_64-cpu。要在插槽 0、核心 1 插入，需要将列出的属性传给 device_add:

   (QEMU) device_add id=cpu-2 driver=IvyBridge-IBRS-x86_64-cpu socket-id=0 core-id=1 thread-id=0
   {
       "execute": "device_add",
       "arguments": {
           "core-id": 1,
           "driver": "IvyBridge-IBRS-x86_64-cpu",
           "id": "cpu-2",
           "socket-id": 0,
           "thread-id": 0
       }
   }
   {
       "return": {}
   }
   (QEMU)
   

5. 可选运行 query-cpus-fast 查看详情:

   (QEMU) query-cpus-fast
   {
       "arguments": {}
       "execute": "query-cpus-fast",
   }
   {
       "return": [
           {
               "cpu-index": 0,
               "props": {
                   "core-id": 0,
                   "socket-id": 0,
                   "thread-id": 0
               },
               "qom-path": "/machine/unattached/device[0]",
               "target": "x86_64",
               "thread-id": 28957
           },
           {
               "cpu-index": 1,
               "props": {
                   "core-id": 1,
                   "socket-id": 0,
                   "thread-id": 0
               },
               "qom-path": "/machine/peripheral/cpu-2",
               "target": "x86_64",
               "thread-id": 29095
           }
       ]
   }
   (QEMU)
   

vCPU 热移除

从 qmp-shell 调用 device_del:

(QEMU) device_del id=cpu-2
{
    "arguments": {
        "id": "cpu-2"
    }
    "execute": "device_del",
}
{
    "return": {}
}
(QEMU)

备注

热移除需要客户机配合，因此此命令只是请求，不保证立即移除。客户机收到 系统控制中断（SCI），调用相关 vCPU 的 ACPI 处理程序，再由内核将 CPU 下线并通知 QEMU 移除。