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@linux.intel.com>
Acked-by: Kristen Carlson Accardi <kristen@linux.intel.com>
Cc: 4.1+ <stable@vger.kernel.org> # 4.1+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 3af9dd7332e6927d8dd860b5af410fba738bff4a..aa33b92b3e3e8866345e9893e3b0a880b8b1a17a 100644 (file)
--- 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);