Re: [Xen-devel] [PATCH] use per-cpu variables in cpufreq

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 31/05/2011 02:51, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:

>> 
>> Well, there is a difference between logical and physical cpu hotplug. Xen is
>> capable of bringing CPUs online and offline without them actually being
>> physically plugged/unplugged from the mainboard. Indeed our physical hotplug
>> support is relatively new and I would suspect not much used (and it supports
>> only physical insertion, not removal!).
>> 
>> Frankly there are a number of questions around CPUs that are physically
>> plugged in after boot:
>>  * How does per-CPU ACPI state like PM info get set up?
> 
> A hotplug-able cpu still has an ACPI CPU object in DSDT table, which may exist
> in original DSDT table, or dynamically loaded later upon hotplug event. Once
> dom0 ACPI recognizes a new CPU object, it will notify Xen about discovered
> pm information.

Thanks. I guessed there was probably some magic for this.

 -- Keir

>>  * In a system where TSCs are otherwise all perfectly in sync, does the
>> firmware help us by setting up the new CPUs' TSCs likewise?
> 
> Here what firmware can do is similar to what Xen can do, which can't ensure
> you a truly synchronized TSC on new CPU.
> 
> Thanks
> Kevin
> 



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