Re: [Xen-devel] Core parking feature enable

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 01.03.12 at 15:31, "Liu, Jinsong" <jinsong.liu@xxxxxxxxx> wrote:
> Jan Beulich wrote:
>>>>> On 01.03.12 at 12:14, "Liu, Jinsong" <jinsong.liu@xxxxxxxxx> wrote:
>>> Unfortunately, yes, though cumbersome is not basic reason user space
>>> approach is not preferred. Core parking is a power management staff,
>>> based on dynamic physical details like cpu topologies and maps owned
>>> by hypervisor. It's natural to implement 
>> 
>> CPU topology is available to user space, and as far as I recall your
>> hypervisor patch didn't really manipulate any maps - all it did was
>> pick what CPU to bring up/down, and then carry out that decision.
> 
> No. threads_per_core and cores_per_socket exposed to userspace is pointless 
> to us (and, it's questionable need fixup).

Sure this would be insufficient. But what do you think did
XEN_SYSCTL_topologyinfo get added for?

> Core parking depends on following physical info (no matter where it 
> implement):
> 1. cpu_online_map;
> 2. cpu_present_map;
> 3. cpu_core_mask;
> 4. cpu_sibling_mask;
> all of them are *dynamic*, especially, 3/4 are varied per cpu and per 
> online/offline ops.

Afaict all of these can be reconstructed using (mostly sysctl)
hypercalls.

Jan


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