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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: b34ef932d7 (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>
This commit is contained in:
Srinivas Pandruvada 2015-10-15 12:34:21 -07:00 committed by Rafael J. Wysocki
parent 25cb62b764
commit 8e601a9f97
1 changed files with 5 additions and 0 deletions
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5
drivers/cpufreq/intel_pstate.c
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@ -776,6 +776,11 @@ static inline void intel_pstate_sample(struct cpudata *cpu)
local_irq_save(flags); local_irq_save(flags);
rdmsrl(MSR_IA32_APERF, aperf); rdmsrl(MSR_IA32_APERF, aperf);
rdmsrl(MSR_IA32_MPERF, mperf); rdmsrl(MSR_IA32_MPERF, mperf);
if (cpu->prev_mperf == mperf) {
local_irq_restore(flags);
return;
}
tsc = rdtsc(); tsc = rdtsc();
local_irq_restore(flags); local_irq_restore(flags);