linux-kernel - Re: [PATCH 4/5] intel_pstate: Remove C0 tracking

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Message-ID: <5370318D.2010309@semaphore.gr>
Date:	Mon, 12 May 2014 05:27:25 +0300
From:	Stratos Karafotis <stratosk@...aphore.gr>
To:	rjw@...ysocki.net, dirk.brandewie@...il.com,
	Dirk Brandewie <dirk.j.brandewie@...el.com>
CC:	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH 4/5] intel_pstate: Remove C0 tracking

Hi,

On 12/05/2014 05:14 πμ, Stratos Karafotis wrote:
> From: Dirk Brandewie <dirk.j.brandewie@...el.com>
> 
> Commit fcb6a15c intel_pstate: Take core C0 time into account for core busy
> introduced a regression referenced below.  The issue with "lockup"
> after suspend that this commit was addressing is now dealt with in the
> suspend path.
> 
> References:
>    https://bugzilla.kernel.org/show_bug.cgi?id=66581
>    https://bugzilla.kernel.org/show_bug.cgi?id=75121
> 
> Reported-by: Doug Smythies <dsmythies@...us.net>
> Signed-off-by: Dirk Brandewie <dirk.j.brandewie@...el.com>
> ---
>  drivers/cpufreq/intel_pstate.c | 13 +------------
>  1 file changed, 1 insertion(+), 12 deletions(-)
> 
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index bb20881..4c26faf 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -59,7 +59,6 @@ struct sample {
>         int32_t core_pct_busy;
>         u64 aperf;
>         u64 mperf;
> -       unsigned long long tsc;
>         int freq;
>  };
> 
> @@ -100,7 +99,6 @@ struct cpudata {
> 
>         u64     prev_aperf;
>         u64     prev_mperf;
> -       unsigned long long prev_tsc;
>         struct sample sample;
>  };
> 
> @@ -561,46 +559,37 @@ static inline void intel_pstate_calc_busy(struct
> cpudata *cpu,
>                                         struct sample *sample)
>  {
>         int32_t core_pct;
> -       int32_t c0_pct;
> 
>         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));
> -
>         sample->freq = fp_toint(
>                 mul_fp(int_tofp(cpu->pstate.max_pstate * 1000), core_pct));
> 
> -       sample->core_pct_busy = mul_fp(core_pct, c0_pct);
> +       sample->core_pct_busy = core_pct;
>  }
> 
>  static inline void intel_pstate_sample(struct cpudata *cpu)
>  {
>         u64 aperf, mperf;
> -       unsigned long long tsc;
> 
>         rdmsrl(MSR_IA32_APERF, aperf);
>         rdmsrl(MSR_IA32_MPERF, mperf);
> -       tsc = native_read_tsc();
> 
>         aperf = aperf >> FRAC_BITS;
>         mperf = mperf >> FRAC_BITS;
> -       tsc = tsc >> FRAC_BITS;
> 
>         cpu->sample.aperf = aperf;
>         cpu->sample.mperf = mperf;
> -       cpu->sample.tsc = tsc;
>         cpu->sample.aperf -= cpu->prev_aperf;
>         cpu->sample.mperf -= cpu->prev_mperf;
> -       cpu->sample.tsc -= cpu->prev_tsc;
> 
>         intel_pstate_calc_busy(cpu, &cpu->sample);
> 
>         cpu->prev_aperf = aperf;
>         cpu->prev_mperf = mperf;
> -       cpu->prev_tsc = tsc;
>  }
> 
>  static inline void intel_pstate_set_sample_time(struct cpudata *cpu)
> --
> 1.9.0
> 
> --
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> 

With this patch, my CPU (Core i7-3770 @ 3.90GHz) seems to never use lowest
frequencies. Even on an idle system I get always ~2GHz. Normally,
on an idle system it used to be 1.6GHz.
On very small loads (mp3 decoding) the CPU goes up to 2.7G GHz (it used to
be 1.6GHz)

Reverting, this patch on my local build, the problem is resolved.


Thanks,
Stratos Karafotis

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