The Quest for More Processing Power, Part Two: "Multi-core and multi-threaded gaming"
by Johan De Gelas on March 14, 2005 12:05 AM EST- Posted in
- CPUs
Conclusion
Writing multithreaded code means much higher software development costs while CPU development gets easier and thus cheaper (compared to even more complex superscalar CPUs). No wonder that the CPU developers are very motivated to hype the multi-core route, but the software development community is probably less enthusiastic.Intel and other manufacturers should not simply push the costs of getting higher performance onto the software developers. Because, in the end, it will be the consumer who will pay the final price: either more money or buggier software with more crashes and hangs. One way that Intel and others can help to keep multithreaded development costs under control while offering increasing CPU performance is to keep investing in ILP and thus higher IPC cores; another option is to improve the interCPU communications.
The easiest part of multithreading is using threads that are running completely independent, that don't share any data. But this source of threading is probably already being used almost to the fullest. In order to tap into a new source of multithreading, such as the largely unused potential of multithreaded AI, Phyics and animation, it is important that developers don't have to worry about interthread messaging and synchronization lowering performance.
Very fast interprocessor communications to make sure that thread synchronization comes with little overhead will give a bigger incentive to developers to invest the extra time in multithreading.
Gabriele Svelto:[4]
"Most of the current multi-threaded software is developed with an eye at keeping inter-thread messaging and synchronization as low as possible because both have a significant cost. This cost will be lowered by an ordered of magnitude by multiple cores on a single die giving in turn more flexibility for the programmers.The Pentium-D and Pressler are examples of how not to do it: just slap two CPUs on the same die and call it a day. High clocked single cores like the upcoming Athlon 64 FX-57 will eat these massive chips for lunch in almost all benchmarks while consuming less energy. With the exception of some special far-fetched benchmarks, it will be pretty hard to justify the reason behind these dual cores.
Applications which got low speed-ups by going multi-threaded due to the overhead of fine-grained locking mechanisms will be able to exploit multiple-processors with fast interprocessor communications much better."
Luckily, Intel's Yonah and AMD's Dual Athlon 64 cores show that better multi-core CPUs are on the way. At that point in time, we are entering the multi-core engine for real. And we can only applaud that because it unleashes a massive amount of CPU power upon the developers.
References
[1] Intel multi-core briefingStephen L. Smith, Vice President Digital Enterprise group, IDF Spring 2005
[2] Unreal 3 engine
http://www.unrealtechnology.com/html/technology/ue30.shtml
[3] Galactiv Cilivisations
http://www.galciv.com/index.asp?c=1&u=0
[4] Gabriele Svelto on dualcore CPUs
http://www.aceshardware.com/forums/read_post.jsp?id=20270&forumid=2
Facebook
Twitter
RSS
49 Comments
View All Comments
ChronoReverse - Tuesday, March 15, 2005 - link
Eh? 20% speed reduction? The dual-core sample in the new post was running at 2.4GHz (FX-53). Sure it's not FX-55 speeds but it's still faster than most everything.kmmatney - Monday, March 14, 2005 - link
edit - I just read some of the above posts. Yes, I agree that dual core can be more efficent than dual cpu. However you have about a 20% reduction in core speed which the dual core optimizations will have to overcome, when compared to a single core cpu.kmmatney - Monday, March 14, 2005 - link
For starters, why would dual core be any different than dual cpu? One of the Quake games (quake 3?) was able to make use of a second cpu, and the gain was very minimal. I'm not even sure Id bothered with dual cpu use for Doom3. If everybody has dual core cpu's, then obviously more work would be done to make use of it, but we've had dual cpu motherboards for a long time already.Verdant - Monday, March 14, 2005 - link
there is no one who (has a clue) doubts that you will see an ever increasing level of cores provide an ever increasing level of performance, in fact i would not be surprised if the Mhz races of the 90s become the "number of core" races of this decade.but i think the one line that really hit the nail on the head is the one about a lack of developer tools.
writting a lower level multi-threaded application is extremely difficult, game developers aren't using tools like java or c# where it is a matter of enclosing a section of code in a synchronized/lock block, throwing a few wait() calls in and launching their new thread. - the performance of these platforms just isn't there.
for consideration - a basic 2 thread bounded buffer program in C is easily 200 lines of code, while it can easily be done in a language like C# in about 20.
developers are going to need to either: move to one of these new languages/platforms and take the performance hit, develop a new specialized platform/language, or they will most likely go bankrupt with the old tools.
the other thing that may have some merit - is a compiler that can generate multi-threaded code from single thread code, however to have any sort of real effect it will need to have an enormous amount of research poured into it, as automatically deciding un-serializable tasks is a huge AI task. Intel's current compiler obviously is many years away from the sort of thing i am talking about.
Doormat - Monday, March 14, 2005 - link
#20/#29:The AMD architecture is different than Intels dual core architecture.
AMD will have a seperate HTT link between chips (phy layer only) for intercore communication, and a seperate link to the memory arbitor/access unit.
Whereas intel (when they opt for two seperate cores, two seperate pieces of silicon) will have a link between the two processors, but its is a bus, and not point-to-point, and also will share that bus with all traffic out to the northbridge/mch. Memory traffic, non-DMA I/O traffic, etc.
In other words, AMD has a dedicated intercore comm channel via HTT while Intel does not. This will affect heavily interconnected threads.
saratoga - Monday, March 14, 2005 - link
"Unless you hit a power and/or heat output wall.Tell nVidia that parallell GPUs are bad, they alreay sell their SLI solution for dual-GPU computers."
Multicore doesn't make much sense for GPUs because its not cost effective, and because GPUs do not have the same problems as CPUs. With a GPU you can just double the number of pipelines and your throughput more or less doubles (though bandwidth can be an issue here), and for a fraction the cost of two discreet boards or two seperate GPUs. That approach doesn't work well with CPUs, hence the interest in dual core CPUs.
"Isn't a high IPC-count also a form of parallelism? If so, then beyond a certain count won't it be just as hard to take advantage of a high IPC-count."
Yup. High IPC means you have a high degree of instruction level parallelism. Easily multithreaded code means you have a high degree of thread level parallelism. They each represent part of the parallelism in a piece of code/algorythm, etc.
Fricardo - Monday, March 14, 2005 - link
"While Dual core CPUs are more expensive to manufacture, they are far more easier to design than turning a single core CPU into an even more wider complex CPU issue."Nice grammer ;)
Informative article though. Good work.
suryad - Monday, March 14, 2005 - link
Dang...good thing I have not bought a new machine yet. I am going to stick with my Inspiron XPS Gen1 for a good 3-4 years when my warranty runs out before I go run out and by another top of the line laptop and a desktop.It will be extremely interesting how these things turn out. Things had been slowing down quiet a lot in the technology envelope front last year but AMD with its FX line of processors were giving me hope...now dual cores...I want an 8 cored AMD FX setup. I think beyond 8 the performance increases will be zip.
I am sure by the end of 2006 we will have experienced quiet a massive paradigm shift with multi cored systems and software taking advantage of it. I am sure the MS DirectX developers for WinFX or DirectX Next or WGF 1.0 or whatever the heck it is called are not going to be sitting on their thumbs and not fixing up the overheads associated as mentioned in the article with the current Direct3D drivers. So IMHO we are going to see a paradigm shift.
Good stuff. And as far as threads over processes, I would take threads, lightweight...thats the main thing. Threading issues are a pain in the rear though but I am quiet confident that problem will be taken care of sooner or later. Interesting stuff.
Great article by the way. Tim Sweeney seems quiet humble for a guy with such knowhow. I wonder if Doom's next engine will be multithreaded. John Carmack i am sure is not going to let the UE 3.0 steal all the limelight. What I would love to see is the next Splinter Cell game based on the UE 3.0 engine. I think that would be the bomb!!
stephenbrooks - Monday, March 14, 2005 - link
In the conclusion - some possibly bad wording:--[The easiest part of multithreading is using threads that are running completely independent, that don't share any data. But this source of threading is probably already being used almost to the fullest.]--
It'll still provide large performance increases when you go to multi-cores, though. You can't "already use" the concept of little-interacting threads when you don't have multiple cores to run them on! This is probably actually one of the more exciting increases we'll see from multi-core.
The stuff that needs a lot of synchronising will necessarily be a bit of a compromise.
Matthew Daws - Monday, March 14, 2005 - link
#26: I don't think that's true:http://www.anandtech.com/tradeshows/showdoc.aspx?i...
This suggests (and I'm certain I've read this for a fact elsewhere) that each *core* has it's own cache: this means that cache contention will still be an issue, as it is in dual-CPU systems. I'm not sure about the increased interconnection speed: it would certainly seem that this *should* increase, but I've also read that, in particular, Intel's first dual-core chips will be a real hack in regards to this.
In the future, sure, dual-core should be much better than dual-cpu.
--Matt