Re: Xen Platform QoS design discussion

["Xu, Dongxiao" <dongxiao.xu@intel.com>]

> -----Original Message-----
> From: Jan Beulich [mailto:jbeulich@suse.com]
> Sent: Thursday, May 29, 2014 3:02 PM
> To: george.dunlap@eu.citrix.com; Xu, Dongxiao
> Cc: andrew.cooper3@citrix.com; Ian.Campbell@citrix.com;
> xen-devel@lists.xen.org
> Subject: Re: RE: [Xen-devel] Xen Platform QoS design discussion
> 
> >>> "Xu, Dongxiao" <dongxiao.xu@intel.com> 05/29/14 2:46 AM >>>
> >I think Jan's opinion here is similar to what I proposed in the beginning of this
> thread.
> >The only difference is that, Jan prefers to get the CQM data per-socket and
> per-domain
> >with data copying, while I proposed to get the CQM data per-domain for all
> sockets
> >that can reduce the amount of hypercalls.
> 
> I don't think I ever voiced any preference between these two. All I said it
> depends on
> prevalent usage models, and to date I don't think I've seen a proper analysis of
> what
> the main usage model would be - it all seems guesswork and/or taking random
> examples.
> 
> What I did say I'd prefer is to have all this done outside the hypervisor, with the
> hypervisor just providing fundamental infrastructure (MSR accesses).

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.
 
Thanks,
Dongxiao
 

> 
> Jan