What allows the cores of the 360 to process two threads simultaneously?

[Hyperlite]

Text

"Today we can confirm that the Xbox 360 processor is a simultaneous multithreading (SMT) processor, meaning it can execute several threads at the same time. Specifically, each of the three cores can process two threads at time, thus making the Xbox 360 CPU a six-thread per clock cycle system making the chip look like six conventional processors for applications. This will allow multiple applications to run independently on different cores or a single multithreaded application to perform multiple tasks all at once. "


I understand the significance, but what allows these cores to do this? is it something like an advanced form of Hyperthreading, except it splits clock cycles 50/50 instead of just using unused ones?

 

[dmens]

It's the same thing as HT... but I'll let carlosd tell you how much better it is, LOL!

 

[cubeless]

os... this is a simplification, but a single die with multiple cores can be handled by the os like multiple chips... each core has it's own registers, cache, etc... the os schedules work (hopefully) equally between cores... it's often more efficient to keep the same kind of work in a core since you don't have to swap cache or go to off chip memory as often...

none of this is new and/or (too) amazing of itself... smp systems just used to have to use multiple cores on multiple chips due to the die sizes... as they shrink the dies (dice?) we'll get more and more cores per cpu, most likely, because overall it's probably easier to just give every task a core than it is to keep clocking individual cores faster... until the scheduling overhead uses up too much of the power (which is the bane of all smp systems)...

 

[BrownTown]

The Xbox360 has 3 cores and can process 6 threads. I am pretty sure he is asking about each of the threee cores haveing SMT, not just that it is a multi core processor. But basically it is the exact same as hyperthreading, when instructions from one thread are stalled it will try to issue instructions from a different thread. This was around way before Intel put it into the P4 and labeled it "HyperThreading"

 

[Shenkoa]

Nothing amazing here.

 

[Acanthus]

SMT and hyperthreading are the same thing. Intel just tossed a marketing name on it.

 

[Hyperlite]

Ah, i see. Thats what i figured. I knew it wasn't a revolutionary technology or anything, i just wanted some clarification. thanks for the info everyone.

 

[zephyrprime]

Originally posted by: BrownTown
when instructions from one thread are stalled it will try to issue instructions from a different thread.

That's true but the technology in the xbox 360 & intel HT can do more than that. They can actually divvy up execution units in a given pipeline stage to different threads thuns truly executing more than one thread at the same time. This is called fine grained SMT (as opposed to coarse grained smt which is what you described). Both forms of smt have been around for a long time.