Re: [PATCH V2 1/5] ara virt interface of perf to support kvm guest os statistics collection in guest os

[Jes Sorensen <Jes.Sorensen@redhat.com>]

On 06/22/10 11:31, Peter Zijlstra wrote:
> On Tue, 2010-06-22 at 17:29 +0800, Zhang, Yanmin wrote:
>> On Tue, 2010-06-22 at 10:00 +0200, Jes Sorensen wrote:
>>> On 06/22/10 09:55, Peter Zijlstra wrote:
>>>> On Tue, 2010-06-22 at 15:47 +0800, Zhang, Yanmin wrote:
>>>>> Besides the para virt perf interface, I'm also considering the direct exposition
>>>>> of PMU hardware to guest os. 
>>>>
>>>> NAK NAK NAK NAK, we've been over that, its not going to happen, full
>>>> stop!
>>>>
>>>> Use MSR read/write traps and host perf to emulate the hardware. In some
>>>> cases we could allow the reads without trap but that's a later
>>>> optimization.
>>>
>>> I believe whats meant here is a PMU compatible interface which is
>>> partially emulated. Not a handover of the PMU.
>> Right. We need capture all write to PMU MSR and allows guest os to read MSR directly.
> 
> That latter is not possible, only in a subset of cases can you allow
> that read.

Avi's suggestion of using virtual MSRs makes a ton of sense for this
though, and it makes it possible to switch direct access on/off for the
cases where direct access is possible, and go emulated when it isn't.

Cheers,
Jes