Hyper-Threading - Pros & Cons

Thus far we have a technology that offers an order of magnitude improvement in execution unit utilization but what sort of drawbacks are there to Hyper-Threading?

Fundamentally we still only have one CPU and one set of execution units, so if the OS dispatches two threads that contend for identical resources in the CPU then HT could reduce performance.

In the earlier versions of Hyper-Threading, there were some pretty significant performance drops in desktop applications with it enabled. Luckily through revision after revision of the technology and through the addition of a few new components (flip back a few pages to see what's new) the vast majority of applications will see a performance increase or no performance loss at all.

Over the past several months Intel has been testing various applications and how their performance changes with Hyper-Threading enabled:

The question here is can we validate these results? We'll focus on where Hyper-Threading improves performance shortly, but we want to make sure that enabling HT is not going to reduce performance first:

It looks like Intel was able to deliver on their claims, most users should have no problem leaving Hyper-Threading enabled as it won't reduce performance. In fact, other than in Content Creation Winstone 2002, we saw some pretty decent performance gains with HT enabled which leads us to the next point of investigation - where will HT improve performance?

Hyper-Threading - How it Works (continued) Hyper-Threading - Pros & Cons (continued)

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