commit 8e601a9f97a00bab031980de34f9a81891c1f82f upstream.
Backport to 4.2-stable tree
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.
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
---
drivers/cpufreq/intel_pstate.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index fcb929e..aba2117 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -766,6 +766,11 @@ 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 = native_read_tsc();
local_irq_restore(flags);
--
1.9.3
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