Why does xbox360 core only support 2 threads when x86 chips

[ralexand]

support as many as you throw at it. What am I missing there?

 

[DuckThor Evil]

Re: Why does xbox360 core only support 2 threads when x86 ch

support as many as you throw at it. What am I missing there?

That means simultaneous thread, Intel Hyperthreading models also support 2, all the other X86 only support one at time.

 

[Npl]

Software Threads != Hardware Threads. The later are running simultan, the former are just switched fast enough to make you believe they are running at the same time

 

[ralexand]

Thanks for the clarification guys. So the xenon is able to run two threads simultaneously without affecting the performance of the other thread running on the same core.

 

[carpediem]

Thanks for the clarification guys. So the xenon is able to run to threads simultaneously without affecting the performance of the other thread running the same core.

6 of them, as far as I have understood.

 

[rendezvous]

Thanks for the clarification guys. So the xenon is able to run to threads simultaneously without affecting the performance of the other thread running the same core.

No not really.

There are three cores and each core can run tow threads simultaniously.

The two threads running on the same core still shares the execution units so each thread will generally not run at the same speed as if it wouldn't have to share units with the other thread.
Sharing the caches between the threads can also increase the number of cache misses which will lead to decreased performance.

 

[ERP]

Basically the hardware threads have a zero cost to context switches. Software threads usually have a very large (relatively) thread switch overhead.

The reason this is important is because a large portion of thecomputation resources available to a processor are largely unused because of stalls (usually from memory access). The idea with hyperthreading or similar technologies, is that you can utilise these otherwise wasted cycles on the second hardware thread.

As pointed out in general you will not get 2x the performance, because you now have 2 threads contending for the cache/memory.