Re: [PATCH v4] cpuidle: Add a sysfs entry to disable specific C state for debug purpose.

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 14 Mar 2012 11:24:40 +0800
ShuoX Liu <shuox.liu@intel.com> wrote:

> From: ShuoX Liu <shuox.liu@intel.com>
> 
> Some C states of new CPU might be not good. One reason is BIOS might configure
> them incorrectly. To help developers root cause it quickly, the patch adds a
> new sysfs entry, so developers could disable specific C state manually.
> 
> In addition, C state might have much impact on performance tuning, as it takes
> much time to enter/exit C states, which might delay interrupt processing. With
> the new debug option, developers could check if a deep C state could  impact
> performance and how much impact it could cause.
> 
> Also add this option in Documentation/cpuidle/sysfs.txt.
> 
>
> ...
>
> +#define define_one_state_rw(_name, show, store) \
> +static struct cpuidle_state_attr attr_##_name = __ATTR(_name, 0644, show, store)
>
> ...
>

> +#define define_store_state_function(_name) \
> +static ssize_t store_state_##_name(struct cpuidle_state *state, \
> +		const char *buf, size_t size) \
> +{ \
> +	long value; \
> +	if (!capable(CAP_SYS_ADMIN)) \
> +		return -EPERM; \

Is the capability check required?  The 0644 permissions aren't sufficient?

> +	kstrtol(buf, 0, &value); \
> +	if (value) \
> +		state->disable = 1; \
> +	else \
> +		state->disable = 0; \
> +	return size; \
> +}
>
> ...
>