4 cores and 8 threads

[Tom Jones]

Hyperthreading is enabled or disabled at the BIOS level.  The OS just sees more processors.

Multithreading happens within the OS and allows apps to be "spread out" between processors.  It's multithreading you need the libraries for.

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On Sep 7, 2016, 7:57 PM, at 7:57 PM, Bob Elzer <bob.elzer at gmail.com> wrote:
>Here's where I may put my foot in my mouth.
>
>If I'm not mistaken programs have to be compiled with a hyperthreading
>library in order to take advantage of this.
>
>Or am I wrong?
>
>On Sep 7, 2016 1:27 PM, "Kevin Fries" <kevin at fries-biro.com> wrote:
>
>> I once worked for a company doing ground water modeling for mining
>> operations.  The program did a large series of fourier transformation
>to
>> model the water levels over time... No Hyperthreading!!!
>>
>> Most web servers, mail servers, database servers (depending on your
>number
>> of indexes), are perfectly fine with hyperthreading turned on.
>>
>> Kevin
>>
>> On Sep 7, 2016 2:21 PM, "Carruth, Rusty" <Rusty.Carruth at smartm.com>
>wrote:
>>
>>> Kevin,
>>>
>>>
>>>
>>> Do you have a reference to the ‘heavy use by one process on a cpu
>core
>>> can affect any other process’?  (BTW, Affect, not Effect in this
>case.
>>> This is only going to you, regardless of what it looks like, so this
>is
>>> just between me an you unless you reply all, in which case it goes
>global,
>>> as it were)
>>>
>>>
>>>
>>> In any case, what little experimenting I did a while back indicated
>that,
>>> when Intel hyperthreads, what happens is effectively half of the cpu
>runs
>>> one thread, and the other half runs the other thread.
>>>
>>>
>>>
>>> So, for windows, where it does a TERRIBLE job (or it used to) of
>>> pre-emptive multitasking, having ‘more’ CPUs is better so that the
>OS can
>>> lock one down because it doesn’t know how to share it - thus hiding
>the bug.
>>>
>>>
>>>
>>> In linux, IMHO you should turn multithreading off.
>>>
>>>
>>>
>>> (IIRC, I ran a system with HT on, and looked at BogoMIPS, then ran
>with
>>> HT off, and the BogoMIPS doubled.  I could be remembering wrong, and
>it was
>>> in the early days of HT, so perhaps they’ve “fixed” it)
>>>
>>>
>>>
>>> Rusty
>>>
>>>
>>>
>>> *From:* plug-discuss-bounces at lists.phxlinux.org [mailto:
>>> plug-discuss-bounces at lists.phxlinux.org] *On Behalf Of *Kevin Fries
>>> *Sent:* Wednesday, September 07, 2016 12:51 PM
>>> *To:* Main PLUG discussion list
>>> *Subject:* Re: 4 cores and 8 threads
>>>
>>>
>>>
>>> The big thing to keep in mind is this....
>>>
>>> All threading either at the processor or in code will share a
>resource.
>>> Heavy use by one process on a CPU core can effect any other process
>running
>>> on that core.  Heavy use on one CPU core will not effect the other
>cores.
>>> (sorta, as data bus issues can still occur).
>>>
>>> Most processes use very little actual CPU.  So, between the OS and
>the
>>> multicores, modern computers can push allot of work through
>themselves.
>>>
>>> That said, there are some processes that are highly comparative.
>>> Multicores can actually slow down execution in these cases because
>any type
>>> of multiuse of a resource will encounter administrative overhead. 
>But
>>> these processes are the exception, not the rule.  If you have such
>needs,
>>> turn Hyperthreading off.  Generally leave it on, and the the
>hardware do
>>> its job.
>>>
>>> Kevin
>>>
>>>
>>>
>>> On Sep 7, 2016 1:36 PM, "Jerry Snitselaar" <dev at snitselaar.org>
>wrote:
>>>
>>> On Tue Sep 06 16, Keith Smith wrote:
>>>
>>>
>>>
>>> Hi,
>>>
>>> If an Intel CPU has 4 cores and 8 threads will it look like 8 cores
>to
>>> VirtualBox when assigning resources to a guest?
>>>
>>> If so is there a way to determine which is a tread and which is
>actually
>>> a core?
>>>
>>> Thanks!!
>>> Keith
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>>>
>>>
>>> In addition to the answers already given, you can read
>>> about it in Volume 1 of the Intel Software Developer's Manual,
>>> section 2.2.8.
>>>
>>> http://www.intel.com/content/www/us/en/processors/architectu
>>> res-software-developer-manuals.html
>>>
>>> As to your question, if you have a hyperthreaded CPU it will look
>like
>>> multiple cores and there is no difference between them as far as
>>> you're concerned.
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>>
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