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Hyperthreading Hurts Server Performance?
sebFlyte writes "ZDNet is reporting that enabling Intel's new Hyperthreading Technology on your servers could lead to markedly decreased performance, according to some developers who have been looking into problems that have been occurring since HT has been shipping automatically activated. One MS developer from the SQL server team put it simply: 'Our customers observed very interesting behaviour on high-end HT-enabled hardware. They noticed that in some cases when high load is applied SQL Server CPU usage increases significantly but SQL Server performance degrades.' Another developer, this time from Citrix, was just as blunt. 'It's ironic. Intel had sold hyperthreading as something that gave performance gains to heavily threaded software. SQL Server is very thread-intensive, but it suffers. In fact, I've never seen performance improvement on server software with hyperthreading enabled. We recommend customers disable it.'"
What is the performance gap between dual CPU vs Dual-core?
It's the usual answer: it depends.
We have to get rid of the notion that there is one overall system architecture that is "right" for all computing needs.
For general, every-day desktop use, there should be little difference between a dual CPU SMP box and a dual core box.
I have a small cluster consisting of AMD 64 X2 nodes, and the nodes use the FC4 SMP kernel just fine. All scheduling between CPU's is handled by the OS, and MPI/PVM apps run just as expected when using the configurations suggested for SMP nodes.
In fact, with the dual channel memory model, dual core AMD systems might be a little better than generic dual CPU, since each processor has it's "own" memory.
Computational Chemistry products and services.
That's nonsense. Compilers routinely do loads of optimisations to better suit the underlying hardware. That's why any linux distro that ships binary packages has many flavors of each important or performance sensitive package (specially the kernel, in Debian you'll find images optimised for 386, 586, 686, k6, k7, etc). Is one of the reasons of the existence of Gentoo, also.
So MS had to make a choise: ship a binary optimized for every possible mix of hw (being the processor the most important factor, but not the only one), which is impossible, or ship images compatible with any recent x86 processor/hw... without being specially optimised for any. That's why hyperthreading performance suffers.
This is an important problem on Windows because most of the time you cannot simply recompile the un-optimised software to suit your hardware, as you can in Linux, etc.
(sorry for my bad english)