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

[Tim Gardner]

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 ?

rtg


-- 
Tim Gardner tim.gardner at canonical.com