[systemd-devel] [PATCH] Add the CPU hotplug rule

[Kay Sievers]

On Tue, Sep 2, 2014 at 8:12 AM, Zhenzhong Duan
<zhenzhong.duan at oracle.com> wrote:
> On 2014-9-2 13:55, Kay Sievers wrote:
>>
>> On Tue, Sep 2, 2014 at 5:22 AM, Zhenzhong Duan
>> <zhenzhong.duan at oracle.com> wrote:
>>>
>>> Cpu doesn't get online automaticly after hotplug when we test guest cpu
>>> add/remove in xen env.
>>>
>>> I don't have an baremetal env to test this, but I think it's same.
>>>
>>> The rule is missed in systemd but exist in legacy udev.
>>
>> Udev is not a mechanism to establish an unconditional loop from the
>> kernel back to the kernel. Such rule makes no sense and we never
>> shipped that and will not ship it upstream now.
>>
>> If a device should be unconditionally change its state, the kernel
>> should just do that on its own, and not rely on userspace to do that.

> Thanks for your suggestion. Maybe we should add this patch in our internal
> branch.
>
> In fact, kernel does expect user level to control online/offline of cpus.
> There are two step to make a cpu online, 1. plug it, 2. online it.
>
> Plug doesn't have to be followed by online op.

But you rule does that unconditionally. Shipping such things in udev
rules makes no sense.

Kay