Messages in this thread | | | Date | Thu, 15 Dec 2011 19:57:08 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH v4 0/7] x86: BSP or CPU0 online/offline |
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* Yu, Fenghua <fenghua.yu@intel.com> wrote:
> > We need a debug feature for this: > > CONFIG_DEBUG_BOOT_CPU_OFF=y or such (disabled by default): > > this feature would offline the boot CPU as soon as possible, > > and boot up userspace with the boot CPU offlined. > > I would think the earliest time when CPU0 can be offline is > right after do_initcalls() because do_initcalls() installs > some cpu hotplug notifier. > > But this will change generic code (e.g. add arch hook in > init/main.c or add a new initcall level which is after level > 7s). > > Another way is to offline CPU0 (or any CPU) in /etc/rc.local. > By this way, we don't change kernel. And this is safe, but a > bit later than in kernel. > > Any comment?
I think we should try to do this in the kernel, to keep the debug feature independent of user-space code. This also helps us clean init code from boot CPU assumptions.
Not sure we need a new initlevel - why not just offline the CPU? I suspect the cpu hotplug notifier installation that is done in do_initcalls() should be moved earlier so that the boot CPU can be offlined as early as a secondary CPU is up and running.
Thanks,
Ingo
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