On 14-11-2014 12:59, Le_Forgeron wrote:
> Le 14/11/2014 00:36, Cousin Ricky a écrit :
>> Le_Forgeron <jgr### [at] freefr> wrote:
>>> On 13/11/2014 21:21, Cousin Ricky wrote:
>>>> My hardware is a Dell Inspiron 17R with Intel Core i7 (8 cores).
>>>
>>> Isn't that 4 cores with HT ? (for povray, it would be worth 5 cores, YMMV)
>>
>> I've seen "quad core" in literature not attached to this particular model, but
>> in the POV-Ray statistics, there is a clear 8-to-1 ratio between CPU times and
>> elapsed times.  Does this mean that there are 2 CPUs in each core?
>>
>>
> Sort of... there is two full set of registers in each core, allowing to
> run two code in parallel... as long as they do not need the same
> resources from the core.
>
> at 100% cpu like povray, yes there is a 8:1 ratio between cpu times and
> wall-clock time. Yet, if the scheduler of the operating system is not
> too bad, if you force povray to run on less threads (with -WT<number>
> option), you can get some surprise like -WT8 is not twice faster that -WT4.
>
> With good schedulers, povray -WT4 would run one thread per core, leaving
> the other set of registers idle or used by something else.
>
>
Talking of which, is there a difference between -WT and +WT? I get the 
impression that both are used indiscriminately.

Thomas

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