4 cores and 8 threads

[Kevin Fries]

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/architectures-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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