cores and threads

[Pete Brunet]

Thanks.  I am thinking of buying a new 4 core laptop later this year so
was curious to know if the 8 thread hyperthreading would help that much
over the 4 cores without hyperthreading.  Actually I don't think there
will be a non-hyperthreading option.  I put in an SSD last week and now
I'm compute bound on my 2 core, 2 thread Lenovo T500.  My IO speed would
also increase due to a doubling of my SATA bandwidth.

On 9/18/13 11:03 PM, David Holmes wrote:
> On 19/09/2013 7:43 AM, Pete Brunet wrote:
>> If a machine has 4 cores and 8 threads will the jdk8 build run faster
>> than one with 4 cores and 4 threads?
>
> All depends on where the bottlenecks are. Given a build is pretty much
> I/O bound I wouldn't expect much difference.
>
>> If so would it be a 2x decrease in build time?
>
> No. The CPU component of the build will be a fraction of the I/O
> component.
>
> Even a compute bound task won't see a 2x difference when run on twice
> the number of hardware threads as they share physical resources in the
> core so can't completely run in parallel.
>
> > Would the build explicitly take advantage of the
>> hyper-threading or would any increase in performance be a side effect?
>
> The build like most other software on the system knows nothing about
> processors, cores and (hyper)-threads. The OS presents a model where
> all of those things represent logical processors and it runs native
> threads on each logical.
>
> Trying to do too much in parallel can easily degrade performance - you
> need to understand how Amdahls Law applies to the computation you are
> doing.
>
> David
>
>
>