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

[Usama Arif]

On 21/02/2023 10:27, David Woodhouse wrote:
> On 21 February 2023 09:49:51 GMT, Oleksandr Natalenko <oleksandr@xxxxxxxxxxxxxx> 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...?