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

[David Herrmann]

Hi

On Fri, Sep 12, 2014 at 5:48 PM, Todd Vierling <tv at duh.org> wrote:
> What we do with those events is udev's rule configuration. Some of
> those actions do involve telling the kernel to do something in
> addition to the original event; see the two examples above (though
> these are not the only ones in common use, obviously). If there were
> no need to configure differing reactions to kernel events, rules.d
> wouldn't exist.
>
> All that is being proposed here is to offer a default reaction to a
> CPU add event -- the configuration for which can be changed by a
> system administrator, distro, or tool just by changing a text file,
> rather than recompiling a kernel.

We don't oppose cpu-hotplug rules, we just want the default to work
_without_ rules. Nobody tells you to recompile your kernel to change
the behavior. We just want the kernel to have sane defaults and then
people can add custom udev scripts on top.

We don't have udev rules to probe drivers on devices. It this is the
_default_ behavior (auto-probing). However, you can use udev to
prevent that and add custom rules to bind custom drivers. Why can't
you do the same for CPUs?
It is ridiculous to call into user-space just to call back into the
kernel without doing _anything_. If you want configuration options,
make the kernel call into user-space *if the configuration is set*.
Otherwise, just skip it.

Thanks
David