Hyper-Threading issues may hurt server performance

ZDNet UK has published an interesting news piece on how Intel's Hyper-Threading technology is apparently causing a significant performance loss when certain server applications are installed. The problem occurs with both SQL Server and Citrix Terminal Server. From the article:
With both SQL Server and Citrix Terminal Server installations, HT-enabled motherboards show markedly degraded performance under heavy load. Disabling HT restores expected levels, according to reports from within the IT industry.
We've always known that enabling Hyper-Threading could dramatically lower performance under certain applications or workloads. A Hyper-Threading-enabled processor shares the same L1 & L2 cache space between two logical processors, which can create problems under the right conditions. What's surprising, however, is that these issues are showing up three years after Intel debuted its HT technology. It'd be interesting to know whether the current HT-related performance loss is the result of incomplete testing or if it's an unavoidable problem.
Tip: You can use the A/Z keys to walk threads.
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