linux-kernel - Re: [PATCH V3] cpuidle: Add a sysfs entry to disable specific C state for debug purpose.

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Date:	Tue, 06 Mar 2012 09:04:14 +0800
From:	Yanmin Zhang <yanmin_zhang@...ux.intel.com>
To:	Henrique de Moraes Holschuh <hmh@....eng.br>
Cc:	ShuoX Liu <shuox.liu@...el.com>,
	Deepthi Dharwar <deepthi@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Brown, Len" <len.brown@...el.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-pm@...ts.linux-foundation.org" 
	<linux-pm@...ts.linux-foundation.org>
Subject: Re: [PATCH V3] cpuidle: Add a sysfs entry to disable specific C
 state for debug purpose.

On Mon, 2012-03-05 at 07:18 -0300, Henrique de Moraes Holschuh wrote:
> On Mon, 05 Mar 2012, ShuoX Liu wrote:
> > @@ -45,6 +46,7 @@ total 0
> >  /sys/devices/system/cpu/cpu0/cpuidle/state1:
> >  total 0
> >  -r--r--r-- 1 root root 4096 Feb  8 10:42 desc
> > +-rw-r--r-- 1 root root 4096 Feb  8 10:42 disable
> >  -r--r--r-- 1 root root 4096 Feb  8 10:42 latency
> >  -r--r--r-- 1 root root 4096 Feb  8 10:42 name
> >  -r--r--r-- 1 root root 4096 Feb  8 10:42 power
> 
> ...
> 
> > diff --git a/drivers/cpuidle/sysfs.c b/drivers/cpuidle/sysfs.c
> > index 3fe41fe..1eae29a 100644
> > --- a/drivers/cpuidle/sysfs.c
> > +++ b/drivers/cpuidle/sysfs.c
> > @@ -222,6 +222,9 @@ struct cpuidle_state_attr {
> >  #define define_one_state_ro(_name, show) \
> >  static struct cpuidle_state_attr attr_##_name = __ATTR(_name, 0444,
> > show, NULL)
> > 
> > +#define define_one_state_rw(_name, show, store) \
> > +static struct cpuidle_state_attr attr_##_name = __ATTR(_name, 0644,
> > show, store)
> > +
> >  #define define_show_state_function(_name) \
> >  static ssize_t show_state_##_name(struct cpuidle_state *state, \
> >  			 struct cpuidle_state_usage *state_usage, char *buf) \
> > @@ -229,6 +232,19 @@ static ssize_t show_state_##_name(struct
> > cpuidle_state *state, \
> >  	return sprintf(buf, "%u\n", state->_name);\
> >  }
> > 
> > +#define define_store_state_function(_name) \
> > +static ssize_t store_state_##_name(struct cpuidle_state *state, \
> > +		const char *buf, size_t size) \
> > +{ \
> > +	int value; \
> > +	sscanf(buf, "%d", &value); \
> > +	if (value) \
> > +		state->disable = 1; \
> > +	else \
> > +		state->disable = 0; \
> > +	return size; \
> > +}
> 
> Isn't this missing a check for capabilities?  Disabling cpuidle states is
> not something random Joe (and IMHO that does mean random capability-
> restricted Joe root) should be doing...
Sorry. Could you elaborate it?

Basically, CPU initialization codes (ACPI on x86) checks the capabilities and
creates the C states in kernel. If we find there are such C states under
/sys/devices/system/cpu/cpuXXX/cpuidle/, we assume CPU supports them.
So here we wouldn't check them again.

> 
> Also, maybe it would be best to use one of the lib helpers to parse that
> value, so that it will be less annoying to userspace (trim blanks, complain
> if there is trailing junk after trimming, etc)?
We would use strict_strtol to parse the value in next version.

Thanks for your kind comments!


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