Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [PATCH] intel_pstate: Change busy calculation to use fixed point math. | Date | Wed, 26 Feb 2014 01:39:25 +0100 |
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On Tuesday, February 25, 2014 10:35:37 AM dirk.brandewie@gmail.com wrote: > From: Dirk Brandewie <dirk.j.brandewie@intel.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@intel.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) >
-- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center.
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