linux-kernel - Re: [PATCH 06/34] perf, kvm: Support the intx/intx_cp modifiers in KVM arch perfmon emulation v2

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Date:	Tue, 23 Oct 2012 14:53:04 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Andi Kleen <andi@...stfloor.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org, acme@...hat.com, eranian@...gle.com,
	Andi Kleen <ak@...ux.intel.com>, avi@...hat.com
Subject: Re: [PATCH 06/34] perf, kvm: Support the intx/intx_cp modifiers in
 KVM arch perfmon emulation v2

On Tue, Oct 23, 2012 at 02:36:05PM +0200, Peter Zijlstra wrote:
> On Thu, 2012-10-18 at 16:19 -0700, Andi Kleen wrote:
> > From: Andi Kleen <ak@...ux.intel.com>
> > 
> > This is not arch perfmon, but older CPUs will just ignore it. This makes
> > it possible to do at least some TSX measurements from a KVM guest
> 
> Please, always CC people who wrote the code as well, in this case that's
> Gleb.
> 
Yes, I missed the v2. Thanks Peter.

> > Cc: avi@...hat.com
> > v2: Various fixes to address review feedback
> > Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> > ---
> >  arch/x86/kvm/pmu.c |   15 +++++++++++----
> >  1 files changed, 11 insertions(+), 4 deletions(-)
> > 
> > diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
> > index cfc258a..81c1632 100644
> > --- a/arch/x86/kvm/pmu.c
> > +++ b/arch/x86/kvm/pmu.c
> 
> > @@ -173,6 +173,11 @@ static void reprogram_counter(struct kvm_pmc *pmc, u32 type,
> >  		.exclude_kernel = exclude_kernel,
> >  		.config = config,
> >  	};
> > +	/* Will be ignored on CPUs that don't support this. */
> > +	if (intx)
> > +		attr.config |= HSW_INTX;
> > +	if (intx_cp)
> > +		attr.config |= HSW_INTX_CHECKPOINTED;
> >  
> >  	attr.sample_period = (-pmc->counter) & pmc_bitmask(pmc);
> >  
> 
> So I forgot how all this worked, but will the KVM emulation not pass
> this straight down to the hardware?
KVM PMU emulation does not talk to HW directly. It creates perf_event to
emulate PMU counter. As far as I see those two will be dropped by
hsw_hw_config() if host HW does not support them.


> 
> Don't we have a problem where we're emulating arch perfmon v1 on AMD
> hardware? On AMD hardware those bits do have meaning.
PMU emulation does not support AMD yet.

--
			Gleb.
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