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【环境信息】
系统：x86物理机 内存：378g
cpu：88核
OS版本： 版本 21.03
[root@localhost ltp]# cat /etc/openEuler-latest
openeulerversion=openEuler-21.03
compiletime=2021-03-04-21-04-09
gccversion=9.3.1-20210204.16.oe1
kernelversion=5.10.0-4.6.0.18.oe1
openjdkversion=1.8.0.282.b08-5.oe1
【问题复现步骤】
echo "0" >/sys/devices/system/cpu/cpu0/online
lscpu
echo "1" >/sys/devices/system/cpu/cpu0/online
lscpu
【预期结果】
echo 0 后lscpu查看cpu0是下线
echo 1 后lscpu查看cpu0是上线
【实际结果】
下线成功，但是上线时执行失败
[root@localhost ltp]# echo "1" >/sys/devices/system/cpu/cpu0/online
-bash: echo: write error: Input/output error
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cpu0 offline 特性默认不启用。
实际场景中，CPU0 承担了很多公共特性，不建议使能 cpu offline。
21.03 中先不默认开启 cpu0 offline。
如果确实需要，或者需要进行调试，可以在启动参数中添加 cpu0_hotplug 进行开启。
cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
Some features depend on CPU0. Known dependencies are:
1. Resume from suspend/hibernate depends on CPU0.
Suspend/hibernate will fail if CPU0 is offline and you
need to online CPU0 before suspend/hibernate.
2. PIC interrupts also depend on CPU0. CPU0 can't be
removed if a PIC interrupt is detected.
It's said poweroff/reboot may depend on CPU0 on some
machines although I haven't seen such issues so far
after CPU0 is offline on a few tested machines.
If the dependencies are under your control, you can
turn on cpu0_hotplug.
合入补丁规避CPU0下线可能引发的问题：
f2c5a15fa2d7 x86: config: disable CONFIG_BOOTPARAM_HOTPLUG_CPU0 by default
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