There are some readable background papers out now, for instance:
http://www.blachford.info/computer/Cells/Cell0.html
As an example, the cell approach to caching is radically different.
Your CPU does a lot of complex run-time guesswork with hard-wired heuristics about how to best organize your code in the different tiers of memory resources available. Cache misses can stall the CPU for long periods; effective utilization of various cache levels is instrumental to performance, yet your interaction with caching mechanisms is weak or non-existent. We typically rely on the CPU to know what to do, or at best give it hints. Many important performance gains in the PC are tied to this "magic CPU" approach. We always expect new machines to run old code (and for that matter, old binaries) faster.
The cell, at last, switches directions. Probably of necessity. Grid computing makes these problems perhaps too difficult to want to solve with such a great reliance on the hardware. The "APU" has no cache in the traditional sense. It has a "local memory," and your code (or your compiler, or your OS, or some interesting combination thereof) manages that.
Virtual Memory hardware, as you know it, isn't present in cell. There is something, of course, but it's different. Apparently, it's simpler, and thus faster.
Though in many ways it's just a continuation of the RISC approach of pushing complexity from the silicon to the software. Software has to do more work, especially the compiler, but the changes reverberate all the way up the stack. On the other hand, if you are willing to do the work, you can win more performance.
On a $50 million video game project, they are willing to do the work. :)
On Mon, 2 May 2005, Devan Lippman wrote:
The CELL is a RISC CPU, why would you want to emulate x86? What I was saying tho was that its based off the power 5 instruction set if I'm not mistaken and shouldn't take much to port to (it'll prolly get done faster than I can get my hands on one).
-- Thanks, Devan Lippman <[EMAIL PROTECTED]>
On 5/2/05, Robert Johnston <[EMAIL PROTECTED]> wrote:On 5/2/05, Devan Lippman <[EMAIL PROTECTED]> wrote:I hope I can get one of these as the CPU for my machine! Been a while since I read that explination but I think that its a series of power CPUs arranged similar to a beowulf cluster all on one chip which means it shouldn't be too far off from existing CPUs that linux will run on in the final presentation to the system. Interesting that they have a screenshot of the demo being replayed in windows media player and not the original demo... still I LOVE SMP and this should have the potential to kill current SMP, AMD and INTEL Multicore all in one hit.
Well, yes, but think of the cost.
Chances are running Dual Dual-core Opteron will be much better "Bang for your buck" than getting a Cell system and having to write an x86 emulator, or porting the entire OS to Cell's instruction set -- Robert "Anaerin" Johnston
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