Re: [Xen-devel] [patch 30/44] xen: Add support for preemption

[tgh <wwwwww4187@sina.com.cn>]

Thank you for your reply
and what about the kernel thread in the xen hypervisor,are there some
instance of kernel threads running in the hypervisor?
I am not sure ,but somewhere I read that there is no kernel thread in
the xen hypervisor ,is it true or what about it?

Thanks in advance


Jeremy Fitzhardinge 写道:
> tgh wrote:
>   
>> Thank for your reply
>> and I still have several questions
>>   
>>     
>>> Yes, that's the normal mode of operation. The hypervisor will timeslice
>>> multiple vcpus onto a single vcpu.
>>>   
>>>     
>>>       
>> that is ,the VM could be preempted by xen,and could xen hypervisor also
>> be preempted to reschedule other vm or xen kernel thread?and are there
>> the counterpart abstractions in xen for kernel thread in linux?
>>   
>>     
>
> Yes, a vcpu in Xen is the same as a task in the kernel. In the same way
> the kernel multiplexes multiple tasks onto your cpu(s), Xen multiplexes
> multiple vcpus onto your cpu(s). This isn't directly visible to the
> guest kernel, in the same way that user processes can't generally
> observe timeslicing.
>
>   
>>> This patch doesn't relate to that; it's whether a Xen Linux guest's
>>> kernel can be preempted to reschedule processes while running under Xen.
>>>   
>>>     
>>>       
>> that is ,the patch makes the guest's kernel, rather than xen, be able to
>> be preempted ,is it right?
>>   
>>     
>
> Yes. Previous to that change, kernel preemption was disabled when
> compiling Xen support in.
>
> J
>
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