Commit e66c1768 authored by Dirk Brandewie's avatar Dirk Brandewie Committed by Rafael J. Wysocki
Browse files

intel_pstate: Change busy calculation to use fixed point math. 

Commit fcb6a15c (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: fcb6a15c (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: default avatarDirk Brandewie <dirk.j.brandewie@intel.com>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent cfbf8d48

drivers/cpufreq/intel_pstate.c

+18 −10
Original line number Diff line number Diff line
@@ -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 void intel_pstate_get_cpu_pstates(struct cpudata *cpu) 
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 = div_fp(int_tofp(sample->mperf), int_tofp(sample->tsc));



	c0_pct = div64_u64(sample->mperf * 100, 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 @@ static inline void intel_pstate_sample(struct cpudata *cpu) 
	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 @@ static inline int32_t intel_pstate_get_scaled_busy(struct cpudata *cpu) 
	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)

CRA Git | Maintained and supported by SUSTech CRA and CCSE