X-bit labs

Intel Developer Forum Spring 2005: Day 2 Coverage (page 11)

Category: Editorial

by Anna Filatova

[ 03/02/2005 | 11:53 PM ]

HyperThreading (HT) and Dual Core Architecture: What Are the Benefits?

Here is the processor architecture scheme with all the major components. Now let’s see how the HT technology will work on different dual and multi core processor designs

If we run an integer thread through the Pentium 4 processor without the HT support, we will see that it goes down the pipeline and gets assigned to the integer execution unit. All the instructions will follow that path.

If we run floating point thread through the same processor the same thing will happen with that only difference that it will go to the floating point execution unit.

  

Now let’s take a look at the same processor with HT and both: integer and floating point threads running at the same time. They will both go down the pipeline and get assigned to the appropriate execution units. You get more work done because you are utilizing resources in a more optimal way.

If we have two floating point threads in the HT enabled processor they both get down the pipeline at the same time and get assigned to the execution unit and if they are using exact same code they will be competing inside the execution unit for the resources. In this case there will not be much of the performance improvement, but this is not necessarily the case, because FP instructions might be using different resources inside that unit.

  

Now let’s take a look at the Pentium D. It does not have HT, but it has two complete execution cores with two integer engines, two floating point engines, etc. And when we have the same two floating point threads they get their own processor floating point unit each and the processing is done faster than in case of a single core processor with HT technology support.

The extreme Edition multi core processor that also has HT can run 4 of these threads at the same time and we will be getting even better performance improvement. But of course, the performance will depend on the system setup, applications that you are running, the amount of supported memory. This is just a general concept: