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 3af9dd7..aa33b92 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -776,6 +776,11 @@
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);