Re: [Xen-devel] [PATCH v6 18/29] xen/x86: allow disabling the emulated pmu

[Roger Pau Monnà <roger.pau@xxxxxxxxxx>]

El 25/09/15 a les 17.13, Jan Beulich ha escrit:
>>>> On 25.09.15 at 17:07, <roger.pau@xxxxxxxxxx> wrote:
>> El 21/09/15 a les 16.48, Boris Ostrovsky ha escrit:
>>> On 09/21/2015 10:36 AM, Jan Beulich wrote:
>>>>>>> On 04.09.15 at 14:08, <roger.pau@xxxxxxxxxx> wrote:
>>>> Hmm - this seems questionable to me: Isn't the vPMU an optional
>>>> feature anyway? I.e. doesn't need separate handling here? Boris?
>>>
>>> It is optional system-wise, not per-guest, which is what I think Roger
>>> is trying to do. I in fact wanted to add ability to disable VPMU per
>>> guest myself.
>>>
>>> However, VPMU has nothing to do with device model so I don't think it
>>> should be part of this series from that perspective.
>>
>> vpmu is enabled globally on the xen command line, there's no way to
>> disable it on a per-guest basis, so AFAICS it will be enabled for
>> HMVlite guests which is wrong because we don't have a vlapic.
> 
> Hmm, Boris specifically enabled vPMU to be available to all three
> kinds of guests, and PVH in it s current shape doesn't have a
> vLAPIC either. So making such a connection seems wrong to me.

IMHO, I would prefer the vPMU support in HVMlite guests to be tied to a
vlapic presence, so we can do it the HVM way instead of having to do
hypercalls.

One think that could work is changing the is_hvm_* calls in vpmu.c to
has_vlapic. This way HVMlite guests could still use the PV vPMU
interface, but once a lapic is enabled we could use the native way.

Roger.


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel