linux-kernel - Re: [PATCH] intel_pstate: Change busy calculation to use fixed point math.

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Date:	Wed, 26 Feb 2014 15:57:05 +0100
From:	Otto Meier <gf435@....net>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>, dirk.brandewie@...il.com
CC:	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	gregkh@...uxfoundation.org, rafael.j.wysocki@...el.com,
	bp@...en8.de, Dirk Brandewie <dirk.j.brandewie@...el.com>
Subject: Re: [PATCH] intel_pstate: Change busy calculation to use fixed point
 math.

On my i3-4330 this patch fixed the problem. works fine

Thanks

Am 26.02.2014 01:39, schrieb Rafael J. Wysocki:
> On Tuesday, February 25, 2014 10:35:37 AM dirk.brandewie@...il.com wrote:
>> From: Dirk Brandewie <dirk.j.brandewie@...el.com>
>>
>> Commit fcb6a15c2e Take core C0 time into account for core busy calculation.
>>
>> Introduced a regression on some processor SKUs supported by
>> intel_pstate. This was caused by 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% 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
>>
>> References:
>>    https://lkml.org/lkml/2014/2/19/626
>>    https://bugzilla.kernel.org/show_bug.cgi?id=70941
>>
>> Signed-off-by: Dirk Brandewie <dirk.j.brandewie@...el.com>
> Queued up as a fix for 3.14.
>
> Thanks!
>
>> ---
>>  drivers/cpufreq/intel_pstate.c | 28 ++++++++++++++++++----------
>>  1 file changed, 18 insertions(+), 10 deletions(-)
>>
>> 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 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)
>>

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