cpufreq: intel_pstate: Fix divide by zero on Knights Landing (KNL)

Orabug: 22623827

commit 8e601a9f97a00bab031980de34f9a81891c1f82f upstream.

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>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 82696471b9c72e4b996e009bb6b4ee432c175582)
Signed-off-by: Dan Duval <dan.duval@oracle.com>

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index e8d16997c5cbcc6c2dee068d616e6f374516422c..1ee2ab58e37d652e03046e5256083bcfa298124a 100644 (file)
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -761,6 +761,11 @@ 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;
+       }
+
        local_irq_restore(flags);
 
        cpu->last_sample_time = cpu->sample.time;