linux-kernel - Re: [PATCH v2 3/3] PM: Introduce Intel PowerClamp Driver

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Date:	Tue, 27 Nov 2012 11:01:32 -0800
From:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:	Joe Perches <joe@...ches.com>
Cc:	Linux PM <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Rafael Wysocki <rafael.j.wysocki@...el.com>,
	Len Brown <len.brown@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Zhang Rui <rui.zhang@...el.com>, Rob Landley <rob@...dley.net>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2 3/3] PM: Introduce Intel PowerClamp Driver

On Mon, 26 Nov 2012 15:27:25 -0800
Joe Perches <joe@...ches.com> wrote:

> On Mon, 2012-11-26 at 06:37 -0800, Jacob Pan wrote:
> > Intel PowerClamp driver performs synchronized idle injection across
> > all online CPUs. The goal is to maintain a given package level
> > C-state ratio.
> 
> trivial notes:
> 
> > diff --git a/drivers/thermal/intel_powerclamp.c
> > b/drivers/thermal/intel_powerclamp.c
> 
> You should still add #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> before any include so that all messages are prefixed with powerclamp:
> 
I missed that. will fix in v4. thanks.
> > +
> > +/* #define DEBUG */
> > +
> > +#include <linux/module.h>
> > +#include <linux/kernel.h>
> []
> > +static void adjust_compensation(int target_ratio, unsigned int win)
> > +{
> > +	int delta;
> 
> It'd be shorter code to use a temporary like
> 
> 	struct powerclamp_calibration_data *d =
> &cal_data[target_ratio];
> 
> > +
> > +	/*
> > +	 * adjust compensations if confidence level has not been
> > reached or
> > +	 * there are too many wakeups during the last idle
> > injection period, we
> > +	 * cannot trust the data for compensation.
> > +	 */
> > +	if (cal_data[target_ratio].confidence >= CONFIDENCE_OK ||
> > +		atomic_read(&idle_wakeup_counter) >
> > +		win * num_online_cpus())
> > +		return;
> > +
> > +	delta = set_target_ratio - current_ratio;
> > +	/* filter out bad data */
> > +	if (delta >= 0 && delta <= (1+target_ratio/10)) {
> > +		if (cal_data[target_ratio].steady_comp)
> > +			cal_data[target_ratio].steady_comp =
> > +				roundup(delta+
> > +
> > cal_data[target_ratio].steady_comp,
> > +					2)/2;
> 
> so that this fits on a single line and becomes:
> 
> 		if (d->steady_comp)
> 			d->steady_comp = roundup(delta +
> d->steady_comp, 2) / 2; 
> 	etc.
> 
looks much better, will fix.
> What clamps target_ratio to the correct range?
> I briefly scanned the code but didn't spot it.
> 
target_ratio is a local variable for set_target_ratio, I did this to
avoid locking in case user wants to change it during computation.
set_target_ratio is clamped by:
        if (set_target_ratio > MAX_TARGET_RATIO)
                set_target_ratio = MAX_TARGET_RATIO;

I guess i could use clamp() macro.

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[Jacob Pan]

-- 
Thanks,

Jacob
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