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

To: "Tian, Kevin" <kevin.tian@xxxxxxxxx>, Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] use per-cpu variables in cpufreq
From: Keir Fraser <keir.xen@xxxxxxxxx>
Date: Tue, 31 May 2011 08:31:20 +0100
Cc: "Liu, Jinsong" <jinsong.liu@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "mark.langsdorf@xxxxxxx" <mark.langsdorf@xxxxxxx>
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Thread-topic: [Xen-devel] [PATCH] use per-cpu variables in cpufreq
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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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