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



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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