Re: [Xen-devel] PVH CPU hotplug design document

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 01/24/2017 02:43 AM, Jan Beulich wrote:
>>>> On 23.01.17 at 19:36, <boris.ostrovsky@xxxxxxxxxx> wrote:
>>>>> I think this should be introduced in your DomU ACPI CPU hotplug series, 
>>>>> and not
>>>>> set for Dom0 until we found a way to perform ACPI vCPU hotplug for Dom0 
>>>>> also.
>>>>>
>>>> Right, although my understanding is that the series is on hold until we
>>>> come to agreement about what to do about dom0. But I guess if we agree
>>>> that we'll have a single ACPI hotplug feature bit then we can go ahead
>>>> with Linux domU patches without waiting for Xen ACPI support.
> How would you test such Linux patches if the Xen side is missing? Or
> am I misunderstanding the statement above?

PV-style hotplug is already supported by the toolstack so that's the
only type of hotplug that domU will use. When ACPI series (with CPUID
flag) gets in then Linux will add code to implement ACPI hotplug based
on whatever leaf/bit we decide to use.

>
>>> My understanding is that the way forward now is to introduce this bit, use 
>>> it
>>> in your series and decide what we do with Dom0 when we get to a point that 
>>> we
>>> can start to test/implement vCPU hotplug there. There's still work to do 
>>> until
>>> we can get to the point of simply booting a static no-hotplug PVHv2 Dom0.
>> Jan, is that how you want to proceed?
> Well, it's not just depending on my opinion, I think. As said, I could
> live with the bimodal approach, but I'm not really happy with it.
> Hence at least a second opinion (perhaps Andrew's, but others'
> input would be more than welcome) should be waited for imo.

I asked you specifically only because you started reviewing v6 at some
point in the past.

But yes, I will wait. As I said, given that we agreed on using CPUID bit
(which I think we did?) lack of ACPI hotplug support doesn't block domU
Linux patches.


-boris


>
>> If yes then do you want me to resubmit the series with CPUID support or
>> should I wait for you to review v6
>> (https://lists.xenproject.org/archives/html/xen-devel/2017-01/msg00060.html)
>> first?
> Well, as you may have seen there've been quite a few patch series
> submitted during the last days. With the desire to also work on my
> own series, and with the need to also work on other stuff, I can't
> really predict when I'd get to look at your or any other patches (it
> is, to be honest, quite a bit discouraging to see so much stuff
> being submitted for review, yet so little participation in reviews,
> but that's not a new/unusual situation at all). Hence I think not
> waiting for review of v6 would be more reasonable, unless
> aforementioned further input gathering turns out to take overly
> long.
>
> Jan
>



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