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

[Peter Zijlstra]

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.
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