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

[Avi Kivity <avi@redhat.com>]

On 02/29/2012 07:05 PM, Joerg Roedel wrote:
> 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?
>
> This is because this function did not run on Fam15h before but now it
> has to so that cpuc->perf_ctr_virt_mask is initialized. The other stuff
> done in this function is setup for northbridge counter. These are not
> yet implemented for Fam15h CPUs so this setup must not run on those
> CPUs. Therefore the check was added.
> Once northbridge counters are implemented for Fam15h this check can go
> away again.
>

Thanks.  Ingo, this had better go through tip.git since most of the
changes are perf related.

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