linux-kernel - Re: [PATCH v2] perf/x86: Fix HO/GO counting with SVM disabled

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Message-ID: <20120229170357.GE11013@redhat.com>
Date:	Wed, 29 Feb 2012 19:03:57 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Joerg Roedel <joerg.roedel@....com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, joro@...tes.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	Stephane Eranian <eranian@...gle.com>,
	David Ahern <dsahern@...il.com>,
	Robert Richter <robert.richter@....com>
Subject: Re: [PATCH v2] perf/x86: Fix HO/GO counting with SVM disabled

On Wed, Feb 29, 2012 at 07:00:09PM +0200, Avi Kivity wrote:
> On 02/29/2012 03:57 PM, Joerg Roedel wrote:
> > It turned out that a performance counter on AMD does not
> > count at all when the GO or HO bit is set in the control
> > register and SVM is disabled in EFER.
> >
> > This patch works around this issue by masking out the HO bit
> > in the performance counter control register when SVM is not
> > enabled.
> >
> > The GO bit is not touched because it is only set when the
> > user wants to count in guest-mode only. So when SVM is
> > disabled the counter should not run at all and the
> > not-counting is the intended behaviour.
> >
> > diff --git a/arch/x86/kernel/cpu/perf_event_amd.c b/arch/x86/kernel/cpu/perf_event_amd.c
> > index 0397b23..67250a5 100644
> > --- a/arch/x86/kernel/cpu/perf_event_amd.c
> > +++ b/arch/x86/kernel/cpu/perf_event_amd.c
> > @@ -1,4 +1,5 @@
> >  #include <linux/perf_event.h>
> > +#include <linux/export.h>
> >  #include <linux/types.h>
> >  #include <linux/init.h>
> >  #include <linux/slab.h>
> > @@ -357,7 +358,9 @@ static void amd_pmu_cpu_starting(int cpu)
> >  	struct amd_nb *nb;
> >  	int i, nb_id;
> >  
> > -	if (boot_cpu_data.x86_max_cores < 2)
> > +	cpuc->perf_ctr_virt_mask = AMD_PERFMON_EVENTSEL_HOSTONLY;
> > +
> > +	if (boot_cpu_data.x86_max_cores < 2 || boot_cpu_data.x86 == 0x15)
> >  		return;
> 
> Why this (boot_cpu_data.x86 == 0x15) change?
> 
I think it is related to .cpu_starting callback now available in
amd_pmu_f15h where previously it wasn't.

--
			Gleb.
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