Re: [Xen-devel] [PATCH 1/3] x86/ACPI: re-park previously parked CPUs upon resume from S3

[Julien Grall <julien.grall@xxxxxxx>]

Hi Jan,

On 6/17/19 7:40 AM, Jan Beulich wrote:
> > > > On 14.06.19 at 18:52, <julien.grall@xxxxxxx> wrote:
> > The title and commit message are a bit odd to read because you are modifying
> > common code but everything is geared towards x86.
> Indeed. There's no caller of {en,dis}able_nonboot_cpus() in Arm code
> at present, afaics. Hence the code changed (but not the file) is truly
> x86-specific at the moment. I've explicitly thought about the
> "inconsistency" between title and contents, but I've deliberately put it
> as is: The change _is_ x86 / ACPI only, _despite_ touching common
> code (and hence needing a REST maintainer ack).
Bear in mind that I have nearly no knowledge of x86, so trying to write 
a commit message fully the x86 way is not going to help me understand 
why this makes sense for everyone (today or in the future).
> > > @@ -207,15 +207,19 @@ void enable_nonboot_cpus(void)
> > >    
> > >        printk("Enabling non-boot CPUs  ...\n");
> > >    
> > > -    for_each_cpu ( cpu, &frozen_cpus )
> > > +    for_each_present_cpu ( cpu )
> > >        {
> > > +        if ( park_offline_cpus ? cpu == smp_processor_id()
> > park_offline_cpus is x86 specific, so it will not build on Arm.
> And that's intentional, even more so that (as said above) Arm doesn't
> call here in the first place. 
Calling and building are two separate things... A function may be built 
even if it is not called.
> And even if it did - whether to do things the
> "new" way would then still (intentionally) depend on whether Arm had
> any way of park_offline_cpus being "true".
Looking again, we are defining park_offline_cpus to false on Arm (see
a6448adfd3 "xen/cpu: Fix ARM build following c/s 597fbb8"). So there are 
no build issue as I first thought.
Cheers,

--
Julien Grall

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