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

[Kay Sievers]

On Tue, Sep 2, 2014 at 5:11 PM, Colin Guthrie <gmane at colin.guthr.ie> wrote:
>
> John Haxby wrote on 02/09/14 10:31:
>> Col, forgive my ignorance, but cpuadd@$name.service seems to imply that
>> you'd have one file or symlink per CPU.  That's going to be unwieldy
>> when you have hundreds of CPUs isn't it?
>
> Not quite. systemd units with an @ in them are a bit special. You have
> one unit file on disk (cpuadd at .service) and you can instantiate
> instances of them via cpuadd at xxx.service where the value xxx is
> available inside the unit and can be passed to scripts or binaries in
> the ExecStart lines via the %i and %I modifiers.
>
> In this case you wouldn't ever enable them individually via explicit
> symlinks (which is valid in some use cases) but udev would defer to
> systemd to start the instance as needed. This is very similar to how the
> built in systemd-rfkill at .service works. See
> /usr/lib/systemd/system/systemd-rfkill at .service. It's instantiated as
> systemd-rfkill at rfkill1.service for example.
>
>
> It's basically the way to pass in the the CPU number or name to the
> service so you can implement that mission critical "only allowing prime
> numbered CPUs on Wednesday" policy ;)

Nice description. :)

But just in case someone thinks of any per-CPU onlining policy
machinery now: We will not ship anything in that area in systemd/udev
upstream. This stuff just belongs into the kernel, like it works for
any other device.

Kay