4 cores and 8 threads

[Bob Elzer]

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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