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 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.

Best,
Wei

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