Re: [PATCH] intel_pstate: Improve initial busy calculation

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

On Friday, May 30, 2014 11:35:57 PM Rafael J. Wysocki wrote:
> On Friday, May 30, 2014 10:10:57 AM dirk.brandewie@gmail.com wrote:
> > From: Doug Smythies <dsmythies@telus.net>
> > 
> > This change makes the busy calculation using 64 bit math which prevents
> > overflow for large values of aperf/mperf.
> > 
> > Cc: <stable@vger.kernel.org> # 3.14.x
> > Signed-off-by: Doug Smythies <dsmythies@telus.net>
> > Signed-off-by: Dirk Brandewie <dirk.j.brandewie@intel.com>
> 
> This doesn't apply for me on top of bleeding-edge.  Is there a patch missing?

The one below does apply, however.  Is that what you meant?

---
drivers/cpufreq/intel_pstate.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 032efe4f7..c034cde 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -563,15 +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 = &cpu->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)