[PATCH 4.2 103/110] cpufreq: intel_pstate: Fix divide by zero on Knights Landing (KNL)

From: Greg Kroah-Hartman
Date: Fri Nov 06 2015 - 15:21:37 EST

4.2-stable review patch. If anyone has any objections, please let me know.


From: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>

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@xxxxxxxxxxxxxxx>
Acked-by: Kristen Carlson Accardi <kristen@xxxxxxxxxxxxxxx>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

drivers/cpufreq/intel_pstate.c | 5 +++++
1 file changed, 5 insertions(+)

--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -766,6 +766,11 @@ static inline void intel_pstate_sample(s
rdmsrl(MSR_IA32_APERF, aperf);
rdmsrl(MSR_IA32_MPERF, mperf);
+ if (cpu->prev_mperf == mperf) {
+ local_irq_restore(flags);
+ return;
+ }
tsc = native_read_tsc();

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