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SubjectRe: [External] Re: [PATCH v9 0/8] Parallel CPU bringup for x86_64

On 21/02/2023 10:27, David Woodhouse wrote:
> On 21 February 2023 09:49:51 GMT, Oleksandr Natalenko <> wrote:
>> On 21.02.2023 10:06, David Woodhouse wrote:
>>> Why does arch/x86/kernel/acpi/sleep.c::x86_acpi_suspend_lowlevel() set
>>> initial_gs = per_cpu_offset(smp_processor_id()) ?
>>> Would it not be CPU#0 that comes back up, and should it not get
>>> per_cpu_offset(0) ?
>> Wanna me try `initial_gs = per_cpu_offset(0);` too?

I think it might be smp_processor_id() and not 0 incase CPU0 was offline
at the point the system was suspended?

> Hm, yes please. There's another one to make zero on the next line up, I think?
>>> Or maybe we should just set up smpboot_control for the CPU to find its
>>> own stuff, *even* on waking. Since the structures are already set up,
>>> it isn't like a clean boot.
>>> If you let it boot in parallel mode, what if you just *remove* the line
>>> that sets smpboot_control=0 ?
>> If the `smpboot_control = 0;` line in arch/x86/kernel/acpi/sleep.c::x86_acpi_suspend_lowlevel() is commented out, and the system is booted in parallel mode, then suspend/resume works.
> Well that's entertaining. Now, can we come up with any theory which doesn't leave us wondering why it ever worked in the first place...?

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