Re: [Qemu-devel] [RFC PATCH v4 01/11] exec: Remove cpu from cpus list during cpu_exec_exit()

[Andreas Färber]

Am 12.11.2015 um 10:30 schrieb Bharata B Rao:
> On Thu, Nov 12, 2015 at 05:11:02PM +0800, Zhu Guihua wrote:
>> Hi Bharata,
>>
>> On 09/09/2015 03:56 PM, Bharata B Rao wrote:
>>> On Wed, Sep 09, 2015 at 03:41:30PM +0800, Zhu Guihua wrote:
>>>> On 09/09/2015 01:52 PM, Bharata B Rao wrote:
>>>>> On Fri, Sep 04, 2015 at 03:31:24PM +1000, David Gibson wrote:
>>>>>> On Thu, Aug 06, 2015 at 10:57:07AM +0530, Bharata B Rao wrote:
>>>>>>> CPUState *cpu gets added to the cpus list during cpu_exec_init(). It
>>>>>>> should be removed from cpu_exec_exit().
>>>>>>>
>>>>>>> cpu_exec_init() is called from generic CPU::instance_finalize and some
>>>>>>> archs like PowerPC call it from CPU unrealizefn. So ensure that we
>>>>>>> dequeue the cpu only once.
>>>>>>>
>>>>>>> Instead of introducing a new field CPUState.queued, I could have used
>>>>>>> CPUState.cpu_index to check if the cpu is already dequeued from the 
>>>>>>> list.
>>>>>>> Since that doesn't work for CONFIG_USER_ONLY, I had to add a new field.
>>>>>>>
>>>>>>> Signed-off-by: Bharata B Rao <address@hidden>
>>>>>> This seems reasonable to me, but I'm wondering how x86 cpu hotplug /
>>>>>> unplug is working without it.
>>>>> x86 hotplug/unplug code currently resides in Zhu's git tree
>>>>> (git://github.com/zhugh/qemu). They are removing the CPU from the list
>>>>> explicitly in x86 CPU's instance_finalize routine.
>>>> Sorry, my git tree is git://github.com/zhuguihua/qemu
>>>>
>>>> Now there was no progress about topology, so we don't know what will happen
>>>> in x86. I am not sure whether we will take this method finally.
>>> Andreas had a presentation on this topic in KVM forum recently.
>>>
>>> Andreas - do you have any updates on the topology and other aspects
>>> of CPU hotplug so that we can align the CPU hotplug work in different
>>> archs accordingly and hope to get it merged in 2.5 time frame ?
>>
>> Do you update the patchset?
>>
>> My work in x86 has stopped for a while, Maybe I can get some ideas from
>> another
>> arch's worker.
> 
> My last version is here:
> https://lists.gnu.org/archive/html/qemu-devel/2015-08/msg00650.html
> 
> I initally started with core level CPU hotplug, moved to socket level hotplug
> based on Andreas' patchset and then moved back again to core level hotplug.
> 
> I was a bit confused about how the generic semantics would evovle and hence
> the work got delayed. I wil be posting the next version of my patchset
> based on core level semantics soon.

What I recall as conclusion from the KVM Forum session and previous
discussions was that pseries would operate on core level (i.e.,
granularity of two SMT threads), whereas your first try was on thread
level and then on socket level.

Regards,
Andreas

> I am hoping that I should be able to get CPU hotplug/unplug included
> in QEMU-2.6 timeframe.

If there are preparatory patches ready for inclusion today, please point
me to them urgently.

Thanks,
Andreas

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