Re: [Xen-devel] [PATCH v4 10/11] x86/intel_pstate: support the use of intel_pstate in pmstat.c

["Wang, Wei W" <wei.w.wang@xxxxxxxxx>]

On 09/09/2015 19:57,  Jan Beulich wrote:
>>> On 09.09.15 at 12:35, <wei.w.wang@xxxxxxxxx> wrote:
> On 09/09/2015 18:10,  Jan Beulich wrote:
>>>> On 09.09.15 at 11:35, <wei.w.wang@xxxxxxxxx> wrote:
>>> Using the drinking vessel analogy, we are not putting milk and water  
>>>into the vessel at the same time. If the producer puts water into the  
>>>vessel, then the consumer simply consumes water; If the producer puts  
>>>milk into the vessel, then the consumer simply consumes milk. I think  
>>>we don't need to worry about what type of drinking is put inside the  
>>>vessel, because the vessel is just an intermediate place holding the 
>>>liquid between the producer and consumer - the consumer has the  
>>>privity of contract with the producer and it has the right logic to 
>>>deal
> with what's inside the vessel.
> 
>> This analogy breaks for a blind: How would he know whether there's 
>> water or
> milk in there? He'd have to try it. 
>>Now what if we use >venom instead of milk in your analogy?
> 
>>Bottom line - the consumer needs to know what kind of data it is to 
>>expect to
> consume.
> 
> There is a contract between the consumer and the producer. In our 
> case, the contract is "p_cpufreq->scaling_driver". Before the right 
> consumer consumes the value of " uint32_t scaling_max_perf ", it goes through 
> the check:
>  +    if (!strncmp(p_cpufreq->scaling_driver,
>  +                  "intel_pstate", CPUFREQ_NAME_LEN) )
> , where "intel_pstate" can be changed to other new driver names 
> (contract) in the future.

> Which is precisely what I already said doesn't scale.

Can you please explain more why it doesn't scale? 
From my point of view, any other future value representation can be passed from 
the producer to the related consumer through this method. 

Best,
Wei


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