[SRU][wily] Fix KNL Intel P State driver divide by zero

[Zhang, Xiong Y]

> On 10/20/2015 02:40 AM, Zhang, Xiong Y wrote:
> > The following commit is from 4.3 kernel which fix devide by zero in
> > intel P state driver on KNL.
> >
> > commit 8e601a9f97a00bab031980de34f9a81891c1f82f
> > Author: Srinivas Pandruvada <srinivas.pandruvada at linux.intel.com>
> > Date:   Thu Oct 15 12:34:21 2015 -0700
> >
> >     cpufreq: intel_pstate: Fix divide by zero on Knights Landing (KNL)
> >
> >     This is a workaround for KNL platform, where in some cases MPERF
> counter
> >     will not have updated value before next read of MSR_IA32_MPERF. In
> this
> >     case divide by zero will occur. This change ignores current sample for
> >     busy calculation in this case.
> >
> >     Fixes: b34ef932d79a (intel_pstate: Knights Landing support)
> >     Signed-off-by: Srinivas Pandruvada
> <srinivas.pandruvada at linux.intel.com>
> >     Acked-by: Kristen Carlson Accardi <kristen at linux.intel.com>
> >     Cc: 4.1+ <stable at vger.kernel.org> # 4.1+
> >     Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
> >
> > diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> > index 3af9dd7..aa33b92 100644
> > --- a/drivers/cpufreq/intel_pstate.c
> > +++ b/drivers/cpufreq/intel_pstate.c
> > @@ -776,6 +776,11 @@ static inline void intel_pstate_sample(struct
> > cpudata *cpu)
> >         local_irq_save(flags);
> >         rdmsrl(MSR_IA32_APERF, aperf);
> >         rdmsrl(MSR_IA32_MPERF, mperf);
> > +       if (cpu->prev_mperf == mperf) {
> > +               local_irq_restore(flags);
> > +               return;
> > +       }
> > +
> >         tsc = rdtsc();
> >         local_irq_restore(flags);
> >
> > thanks
> >
> >
> >
> 
> Wily is now subject to SRU policies. Do you have a bug report for this
> patch ?
[Zhang, Xiong Y] We only have a bug report internally and don't have one on launchpad. Because I don't have KNL hardware, so I couldn't fill one on launchpad and couldn't supply the verification.
> 
> rtg
> 
> 
> --
> Tim Gardner tim.gardner at canonical.com