Le 14-11-14 10:41, Raiford, Michael a écrit :
> On 11/14/2014 5:59 AM, 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.
>>
>>
>
> Yep. Pretty much that. I've noticed that my work computer (core i3, dual
> core) isn't quite as fast as my desktop PC (a Core2 Quad), even though
> it appears to have 4 cores to applications.
>
> I forget exactly what hyperthreading does, but it does give a bit of a
> boost to multi-threaded applications.
>

hyperthreading implement virtual core(s) on a CPU by having two sets of 
registers. You have 1 true core that looks like there are 2. It makes it 
faster to switch between threads.

Alain

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