When HT met MP

Although Hyper-Threading technology could provide some increase (~30%) of performance.
This is done by effective shared resource on the same processor. On Linux and Windows
system, a single HT Processor could found 2 CPU resources. However, since HT technology
makes use of shared resources, the performance of a processor with HT enabled is not as
fast as two processors with HT disabled. Hence, under multiple processors configuration,
if the scheduler of the kernel is not HT-aware, two running tasks may be scheduled on the
two virtual processors of the same physical processor instead of two physical processors.
This is because the kernel view it has 4 processors instead of 2, say, on a dual
HT-processors system. The bad thing is this could make one phyiscal processor saturated
while the other completely idle. In consequence, it makes performance result unpredictable
as the scheduling of running tasks on multiple virtual processors is random since
it treats all processors the same.

The following links shows how Linux kernel be patched in order to solve the imbalance
situation:

• Hyper-Threading speeds Linux
• Patch: "fully HT-aware scheduler" support, 2.5.31-BK-curr

And I wonder how Windows 2000/XP Pro addresses the scheduling problem of SMP with HT...