Re: Xen Platform QoS design discussion

["Jan Beulich" <jbeulich@suse.com>]

>>> Ian Campbell <ian.campbell@citrix.com> 05/30/14 11:11 AM >>>
>On Thu, 2014-05-29 at 10:11 +0100, Jan Beulich wrote:
>> >>> "Xu, Dongxiao" <dongxiao.xu@intel.com> 05/29/14 9:31 AM >>>
>> >Okay. If I understand correctly, you prefer to implement a pure MSR access
>> >hypercall for one CPU, and put all other CQM things in libxc/libxl layer.
>> 
>> >In this case, if libvert/XenAPI is trying to query a domain's cache utilization
>> >in the system (say 2 sockets), then it will trigger _two_ such MSR access
>> >hypercalls for CPUs in the 2 different sockets.
>> >If you are okay with this idea, I am going to implement it.
>>  
>> I am okay with it, but give it a couple of days before you start so that others
>> can voice their opinions too.
>
>Dom0 may not have a vcpu which is scheduled/schedulable on every socket.
>scheduled it can probably deal with by doing awful sounding temporary
>things to its affinity mask, but if it is not schedulable (e.g. due to
>cpupools etc) then that sounds even harder to sort...

But that's why we're intending to add a helper hypercall in the first place. This
isn't intended to be a 'read MSR' one, but a 'read MSR in this CPU'.

Jan