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

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

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 <bharata@linux.vnet.ibm.com>
> >>>>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.

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

Regards,
Bharata.