intel_pstate: Improve initial busy calculation

This change makes the busy calculation using 64 bit math which prevents
overflow for large values of aperf/mperf.

Cc: 3.14+ <stable@vger.kernel.org> # 3.14+
Signed-off-by: Doug Smythies <dsmythies@telus.net>
Signed-off-by: Dirk Brandewie <dirk.j.brandewie@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 8 insertions, 5 deletions

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 2a07588dcbac..db2e45b4808e 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -563,16 +563,19 @@ static void intel_pstate_get_cpu_pstates(struct cpudata *cpu)
 static inline void intel_pstate_calc_busy(struct cpudata *cpu,
                                         struct sample *sample)
 {
-        int32_t core_pct;
+        int64_t core_pct;
+        int32_t rem;
 
-        core_pct = div_fp(int_tofp((sample->aperf)),
-                        int_tofp((sample->mperf)));
-        core_pct = mul_fp(core_pct, int_tofp(100));
+        core_pct = int_tofp(sample->aperf) * int_tofp(100);
+        core_pct = div_u64_rem(core_pct, int_tofp(sample->mperf), &rem);
+
+        if ((rem << 1) >= int_tofp(sample->mperf))
+                core_pct += 1;
 
         sample->freq = fp_toint(
                 mul_fp(int_tofp(cpu->pstate.max_pstate * 1000), core_pct));
 
-        sample->core_pct_busy = core_pct;
+        sample->core_pct_busy = (int32_t)core_pct;
 }
 
 static inline void intel_pstate_sample(struct cpudata *cpu)