Re: [Xen-devel] [PATCH v2 6/9] x86/intel_pstate: the main boby of the intel_pstate driver

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 01.06.15 at 11:12, <wei.w.wang@xxxxxxxxx> wrote:
> On 29/05/2015 16:46, Jan Beulich wrote
>> >>> On 29.05.15 at 10:19, <wei.w.wang@xxxxxxxxx> wrote:
>> > On 26/05/2015 21:58, Jan Beulich wrote
>> >> >>> On 13.05.16 at 09:50, <wei.w.wang@xxxxxxxxx> wrote:
>> >> > +static int intel_pstate_verify_policy(struct cpufreq_policy
>> >> > +*policy) {
>> >> > +    cpufreq_verify_within_limits(policy, policy->cpuinfo.min_freq,
>> >> > +                                     policy->cpuinfo.max_freq);
>> >> > +
>> >> > +    if ( policy->policy != CPUFREQ_POLICY_POWERSAVE   &&
>> >> > +         policy->policy != CPUFREQ_POLICY_PERFORMANCE &&
>> >> > +         policy->policy != CPUFREQ_POLICY_USERSPACE   &&
>> >> > +         policy->policy != CPUFREQ_POLICY_ONDEMAND )
>> >>
>> >> switch()
>> >
>> > How would we use switch() here?
>> 
>>     switch ( policy->policy )
>>     {
>>     case CPUFREQ_POLICY_POWERSAVE:
>> 
>> etc. But I thought that to be obvious, so I'm not sure I understand what you
>> don't understand.
> 
> I thought there would be a special usage of switch() here, but no.
> So, using switch, we will have 
> switch ( policy->policy )
>  {
>    case CPUFREQ_POLICY_POWERSAVE:
>    case CPUFREQ_POLICY_PERFORMANCE:
>    case CPUFREQ_POLICY_USERSPACE:
>    case CPUFREQ_POLICY_ONDEMAND:      
>                                               return 0;
>    case default: 
>                                               return -EINVAL
> }
> 
> Is there a particular reason why we need to change to this style? I think 
> using if() looks more straightforward, since this is just a condition check.

Well, a good compiler will avoid fetching policy->policy anyway at
least when optimizing, but I consider it good practice to guide the
compiler in the right direction (including non-optimized builds).

Jan


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