intel_pstate: Change busy calculation to use fixed point math.
Commit fcb6a15c2e (intel_pstate: Take core C0 time into account for
core busy calculation) introduced a regression on some processor SKUs
supported by intel_pstate. This was due to the truncation caused by
using integer math to calculate core busy and C0 percentages.
On a i7-4770K processor operating at 800Mhz going to 100% utilization
the percent busy of the CPU using integer math is 22%, but it actually
is 22.85%. This value scaled to the current frequency returned 97
which the PID interpreted as no error and did not adjust the P state.
Tested on i7-4770K, i7-2600, i5-3230M.
Fixes: fcb6a15c2e7e (intel_pstate: Take core C0 time into account for core busy calculation)
References: https://lkml.org/lkml/2014/2/19/626
References: https://bugzilla.kernel.org/show_bug.cgi?id=70941
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 e908161..2cd36b9 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -39,9 +39,10 @@
#define BYT_TURBO_RATIOS 0x66c
-#define FRAC_BITS 8
+#define FRAC_BITS 6
#define int_tofp(X) ((int64_t)(X) << FRAC_BITS)
#define fp_toint(X) ((X) >> FRAC_BITS)
+#define FP_ROUNDUP(X) ((X) += 1 << FRAC_BITS)
static inline int32_t mul_fp(int32_t x, int32_t y)
{
@@ -556,18 +557,20 @@
static inline void intel_pstate_calc_busy(struct cpudata *cpu,
struct sample *sample)
{
- u64 core_pct;
- u64 c0_pct;
+ int32_t core_pct;
+ int32_t c0_pct;
- core_pct = div64_u64(sample->aperf * 100, sample->mperf);
+ core_pct = div_fp(int_tofp((sample->aperf)),
+ int_tofp((sample->mperf)));
+ core_pct = mul_fp(core_pct, int_tofp(100));
+ FP_ROUNDUP(core_pct);
- c0_pct = div64_u64(sample->mperf * 100, sample->tsc);
+ c0_pct = div_fp(int_tofp(sample->mperf), int_tofp(sample->tsc));
+
sample->freq = fp_toint(
- mul_fp(int_tofp(cpu->pstate.max_pstate),
- int_tofp(core_pct * 1000)));
+ mul_fp(int_tofp(cpu->pstate.max_pstate * 1000), core_pct));
- sample->core_pct_busy = mul_fp(int_tofp(core_pct),
- div_fp(int_tofp(c0_pct + 1), int_tofp(100)));
+ sample->core_pct_busy = mul_fp(core_pct, c0_pct);
}
static inline void intel_pstate_sample(struct cpudata *cpu)
@@ -579,6 +582,10 @@
rdmsrl(MSR_IA32_MPERF, mperf);
tsc = native_read_tsc();
+ aperf = aperf >> FRAC_BITS;
+ mperf = mperf >> FRAC_BITS;
+ tsc = tsc >> FRAC_BITS;
+
cpu->sample_ptr = (cpu->sample_ptr + 1) % SAMPLE_COUNT;
cpu->samples[cpu->sample_ptr].aperf = aperf;
cpu->samples[cpu->sample_ptr].mperf = mperf;
@@ -610,7 +617,8 @@
core_busy = cpu->samples[cpu->sample_ptr].core_pct_busy;
max_pstate = int_tofp(cpu->pstate.max_pstate);
current_pstate = int_tofp(cpu->pstate.current_pstate);
- return mul_fp(core_busy, div_fp(max_pstate, current_pstate));
+ core_busy = mul_fp(core_busy, div_fp(max_pstate, current_pstate));
+ return FP_ROUNDUP(core_busy);
}
static inline void intel_pstate_adjust_busy_pstate(struct cpudata *cpu)