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

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Message-ID: <20140509014422.GA9855@intel.com>
Date:	Fri, 9 May 2014 09:44:23 +0800
From:	Yuyang Du <yuyang.du@...el.com>
To:	dirk.brandewie@...il.com
Cc:	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	rjw@...ysocki.net, Dirk Brandewie <dirk.j.brandewie@...el.com>
Subject: Re: [PATCH 4/5] intel_pstate: Remove C0 tracking

Hi Dirk,

I don't get why you remove the c0 tracking.  This is my understanding wrong.

Suppose it is removed, then the objective of the PID control is:

delta(aperf) / delta(mperf) * max_pstate / current_pstate

But delta(aperf) / delta(mperf) * max_pstate is the average frequency of the last
time frame, and current_pstate is the last requested frequency, then the
objective is:

last_freq_average / last_requested_freq ==> setpoint

What does it mean, SW satisfaction of freq request? Why control that?

Thanks
Yuyang

> @@ -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;
>  }
--
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