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

[John Haxby]

On 2 Sep 2014, at 06:55, Kay Sievers <kay at vrfy.org> 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.


Kay,

I’m curious.   Are you thinking of 40-redhat.rules in the RHEL6 udev as not being part of the legacy distribution?

Should there be a rule that uses a systemd target to hot-add CPUs to provide the conditional aspect that’s needed?  Am I right in thinking that this is as simple as turning the old redhat rule into something like

ACTION==“add” KERNEL==“cpu[0-9]*” TAG+=“systemd” ENV{SYSTEMD_WANTS}+=“cpuadd.service”

And the corresponding service’s ExecStart is what actually puts the CPU on line?

Sorry for the questions, I’m still trying to find the time to get to grips with systemd — that’s a poor excuse for something that’s been around for some considerable time I know, but be kind to me :)

jch



> 
> Kay