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Hyperthreading causes slowdowns in servers

By Justin Mann

On November 23, 2005, 5:02 AM

It seems that in certain server scenario situations, Intel's Hyperthreading technology can actually drastically hinder performance, resulting in a bogged down server with heavy CPU load not getting much done. The problem stems from the fact that two threads would share the same cache when being executed, and certain threads would cause the cache to be filled with something useless. It apparently degrades performance in these environments so much as to have some people suggesting disabling it.

"It's ironic," said Ibbotson. "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 when running Citrix and our software on the same server.”
HT likely fits much better on the desktop, where this type of scenario is seldom seen. It may be of interest to those who use suites like Vmware, however. Intel has not yet responded to the findings.

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  1. November 23, 2005 10:07 AM
    DragonMaster said:
    Well... I've always been told that hyperthreading was bad. I see it's true!
    Reply
  2. April 18, 2006 10:36 PM
    IanIppolito said:
    I got a 10% boost from hyperthreading...see my test results here: [url]http://rentacoder.com/CS/blogs/real_life_it/archive/200
    /04/18/SQL_Server_2005_performance_testing_with_hyperthrea
    ing_and_MAX_DOP.aspx[/url]The bottom line is to test yourself and see what applies to you.Ian Ippolito
    Reply

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