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Hyper-Threading Speeds Linux
developerWorks writes "The Intel Xeon processor introduces a new technology called Hyper-Threading (HT) that makes a single processor behave like two logical processors. The technology allows the processor to execute multiple threads simultaneously, which can yield significant performance improvement. But, exactly how much improvement can you expect to see? This article gives the results the investigation into the effects of Hyper-Threading (HT) on the Linux SMP kernel. It compares the performance of a Linux SMP kernel that was aware of Hyper-Threading to one that was not." Ah, the joys of high performance.
>was aware of Hyper-Threading to one that was not."
But if you aren't going to use hyper threading you would use a UP (non-SMP) kernel, which would gain you considerable performance. The benefits are not so clear cut as many of the benchmarks show limited benefit from hyperthreading and would perform faster on a uniprocessor kernel.
The results on Linux kernel 2.4.19 show Hyper-Threading technology could improve multithreaded applications by 30%. Current work on Linux kernel 2.5.32 may provide performance speed-up as much as 51%.
while it may not be very useful for a single-user box(it actually looks like it would be a detriment), integrating it into client-server situations would give us some nice boosts in performance. web servers ought to see some real gains with this.
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The pretty detailed (for me anyway) article on Ars Technica concludes that performance on a HyperThreaded CPU will be very much dependant on the application mix. While research like this is useful it will probably always be a try and see scenario.
Like most development shops, we do a great deal of development for multiprocessor machines so we write a lot of multithreaded code. Multithreaded code creates a whole host of new debugging pitfalls that don't show up if the developer is debugging on a single processor workstation. As John Robbins says in his terrific Debugging Applications book, if you are developing a multithreaded application, you better be certain you are doing your debugging in a multiprocessor environment.
From a development standpoint, will a hyperthreaded chip provide an adequate environment in duplicating the behavior of a multi-processor PC well enough that shops can buy cheaper, one CPU machines for development and still be confident in their results? I'm guessing nothing will replace the real thing but I'd be interested in any commentary.
Hyper-Threading Speeds Windows
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WHat you've conveniently snipped out in your trollish post is all of the applications benchmarks showing improvements. If you're not going to run any application code, you might as well shut the machine off and save the marginal stress on the environment.
Most of us have our computers do work and those applications, running on an OS which has *barely* slowed, will be able to do more work in the same amount of time under the HT-aware OS than under one which does not utilize the second, virtual processor.
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If you're running code that's efficient on a P4 (few mis-predicted branches, low cache miss rate, good parallelism, etc.) then HT is pretty much useless.
If you're running code that's inefficient on a P4 (which pays for its high GHz with long pipelines, large latencies, a slow decode stage, and several other drawbacks), then HT can usually paper over a fair percentage of these problems. But remember that HT requires OS support, may require application support, and "your mileage will vary".
It's easy to make up & spread cool- and credible-sounding stuff. Finding & checking hard facts is hard work.
In Europe P4 3.0 with HT costs ~745 euro (+tax)
An Asus A7M for dual Athlon costs ~260 euro (+tax)
Two Athlon XP 2200+ cost ~340 euro (+tax).
Alternatively you can get two Athlon MP 2000+ for
roughly the same money (if you don't trust the
XPs).
Now, please explain to me why would someone
with real SMP needs in mind (and NOT games)
consider the P4 with HT.
P.
P.S. I understand that the prices in the US are
different, but still, it is VERY expensive.
So, in a nutshell, what MS says is: Windows 2000 counts processors in a broken way and requires you to buy licenses for every logical processor, even though you won't get nearly as much processing power as you would if you really had that many physical processors. But rather than fix this bug, we're going to solve the problem by making you buy .NET, which counts processors correctly. So either way, if you're going to use hyperthreading, expect to send us more money.
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Yes, they do something almost exactly like it. Simply buy two processors and a multi-processor motherboard. That defeats the purpose of this technology, of course, but it nearly accomplishes the same thing.
Other than that, well, I'm--still--waiting for Hammer. AMD is dropping a long ways behind Intel. Price is all they've got, and AMD isn't even competeing on price-performance real well at the moment. My guess is that Intel hyperthreaded systems will probably be better price-performance wise than AMD before long--if they aren't already.
I don't believe that's correct.
As I understand it HT can indeed speed up pure integer code (or more generally code that's competing for a single CPU resource). HT will allow another thread to exceute if the current one is waiting on anything from pipeline results to memory access. I believe that modern CPU/memory speed disaparity was one of the driving forces behind it - if one thread gets a cache miss then another may be able to continue executing rather than having to sit idle waiting for main memory.