Re: [Xen-devel] Core parking feature enable

["Liu, Jinsong" <jinsong.liu@xxxxxxxxx>]

Liu, Jinsong wrote:
> Jan Beulich wrote:
>>>>> On 17.02.12 at 18:48, "Liu, Jinsong" <jinsong.liu@xxxxxxxxx>
>>>>> wrote: 
>>> Jan Beulich wrote:
>>>>>>> On 17.02.12 at 09:54, "Liu, Jinsong" <jinsong.liu@xxxxxxxxx>
>>>>>>> wrote:
>>>>> Core parking is a power control feature and it can co-work with
>>>>> NPTM to control system power budget through online/offline some
>>>>> CPUs in the system. These patches implement core parking feature
>>>>> for xen. They consist of 2 parts: dom0 patches and xen hypervisor
>>>>> patches. 
>>>>> 
>>>>> At dom0 side, patches include
>>>>> [Patch 1/3] intercept native pad (Processor Aggregator Device)
>>>>> logic, providing a native interface for natvie platform and a
>>>>> paravirt template for paravirt platform, so that os can implicitly
>>>>> hook to proper ops accordingly; [Patch 2/3] redirect paravirt
>>>>> template to Xen pv ops; [Patch 3/3] implement Xen pad logic, and
>>>>> when getting pad device notification, it hypercalls to Xen
>>>>> hypervisor for core parking. Due to the characteristic of xen
>>>>> continue_hypercall_on_cpu, dom0 seperately send/get core parking
>>>>> request/result; 
>>>>> 
>>>>> At Xen hypervisor side, patches include
>>>>> [Patch 1/2] implement hypercall through which dom0 send core
>>>>> parking request, and get core parking result;
>>>>> [Patch 2/2] implement Xen core parking. Different core parking
>>>>> sequence has different power/performance result, due to cpu
>>>>> socket/core/thread topology. This patch provide power-first and
>>>>> performance-first policies, users can choose core parking policy
>>>>> on their own demand, considering power and performance tradeoff.
>>>> 
>>>> Does this really need to be implemented in the hypervisor? All this
>>>> boils down to is a wrapper around cpu_down() and cpu_up(), which
>>>> have hypercall interfaces already. So I'd rather see this as being
>>>> an extension to Dom0's pCPU management patches (which aren't
>>>> upstream afaict)... 
>>>> 
>>>> Jan
>>> 
>>> It's a design choice. Core parking is not only a wrapper around
>>> cpu_down/up, it also involves policy algorithms which depend on
>>> physical cpu topology and cpu_online/present_map, etc. Implement
>>> core parking at dom0 side need expose all those information to dom0,
>>> with potential issues (like coherence), while dom0 still need do
>>> same work as hypervisor. Our idea is to keep dom0 as ACPI parser,
>>> then hypercall and do rest things at hypervisor side.
>> 
>> Actually, after some more thought, I don't even think this ought to
>> be implemented in the Dom0 kernel, but in user space altogether.
>> Afaict all information necessary is already being exposed.
>> 
> 
> No, user space lack necessary information. If I didn't misunderstand,
> it has some dom0-side dependencies not ready now, like 
> 1. sysfs interface, and exposing xen pcpu topology and maps;
> 2. intecept pad notify and call usermodehelper;
> 3. a daemon to monitor/policy core parking (daemon enable when linux
> run as pvops under xen (kernel acpi_pad disable now), daemon disable
> when linux run under baremetal (kernel acpi_pad enable now))  
> 
> Seems keep same approach as native kernel which handle acpi_pad in
> kernel side (for us, in hypervisor side) is a reasonable choice. Per
> my understanding core parking is a co-work part of NPTM, the whole
> process is basically a remote controller-microengine-bios-kernel
> process, not necessarily involve user action.    
> 

Any comments?

Thanks,
Jinsong
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