From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Wang, Wei W" <wei.w.wang@intel.com>
Subject: Re: [PATCH v4 10/11] x86/intel_pstate: support the use
 of intel_pstate in pmstat.c
Date: Wed, 9 Sep 2015 08:11:16 +0000
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To: Jan Beulich <JBeulich@suse.com>
Cc: "andrew.cooper3@citrix.com" <andrew.cooper3@citrix.com>, "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
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On 24/07/2015 22:16,  Jan Beulich wrote:
>>> On 25.06.15 at 13:17, <wei.w.wang@intel.com> wrote:
> --- a/xen/drivers/acpi/pmstat.c
> +++ b/xen/drivers/acpi/pmstat.c
> --- a/xen/include/public/sysctl.h
> +++ b/xen/include/public/sysctl.h
> @@ -315,8 +315,18 @@ struct xen_get_cpufreq_para {
>      uint32_t scaling_cur_freq;
>  
>      char scaling_governor[CPUFREQ_NAME_LEN];
> -    uint32_t scaling_max_freq;
> -    uint32_t scaling_min_freq;
> +
> +    union {
> +        uint32_t freq;
> +        uint32_t pct;
> +    } scaling_max;
> +
> +    union {
> +        uint32_t freq;
> +        uint32_t pct;
> +    } scaling_min;

>scaling_min and scaling_max should really be of the same type, so that someone wanting to introduce helper functions 
>or pointers to them can hand both interchangeably.

>Also I'm starting to get tired of repeating that it is still unclear how a consumer of the structure will know which of the 
>two fields of the unions are applicable.

Hi Jan,

Probably we don't need a union here. I plan to simply change them to 
uint32_t scaling_max_perf;
uint32_t scaling_max_perf;

Then it's up to the driver to put what kind of value to it. It's like we simply provide a drinking vessel, and it depends on the user to put water or milk into it. In our case, the intel_pstate driver assigns a percentage vale to it (in the "uint32_t" type), and the legacy driver assigns the absolute value to it (in the "uint32_t" type, too).

I will finish this round of revision soon.

Best,
Wei