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>

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 2a07588dcbac9578b0b6056089c66d49395111f1..db2e45b4808ec124be51b64ab9cf303f172e6108 100644 (file)
--- 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)