Re: hyperthreaded processors running on win2k
From: Geoff N. Hiten (SRDBA_at_Careerbuilder.com)
Date: 04/19/04
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Date: Mon, 19 Apr 2004 10:41:57 -0400
Personally, I have had fairly good experience with Hyperthreading. First,
make sure you are on build 816 or later. There were some significant
HT-friendly modifications in that build. The easiest way is to download the
818 security hotfix and apply it. That way, you do not have to open a case
to get it. Regardless, you must be on SP2 or higher to get SQL to count the
processors correctly for licensing purposes.
Finally, 2 virtual HT processors run about 20-30% faster using SQL than the
same processer set to non HT. SQL still counts them as full processors for
parallelism, meaning that you can over-parallel a query and drag system
performance down. I manually set MAX DEGREE OF PARALLELISM (MAXDOP) to no
higher than the actual physical processor count.
-- Geoff N. Hiten Microsoft SQL Server MVP Senior Database Administrator Careerbuilder.com I support the Professional Association for SQL Server www.sqlpass.org "Mark" <maxmann@kc.rr.com> wrote in message news:uyOJwARJEHA.1312@TK2MSFTNGP12.phx.gbl... > > My company is currently deploying new hardware for our new hosting site. We > have all new servers. 4 of them are running Win2k standard server and are > web servers, and 3 of them are win2k advanced servers running SQL Server > 2000. > These servers have dual Xeons, so if hyperthreading is on, win2k sees 4 > procs. > > We have been working on tracking down speed issues for quite a while and > recently realized (by accident) , that the webservers run WAY faster when > hyperthreading is turned off. We are using MS Application Center Test for > load testing, so that's how we determined the performance gain. > > I've been trying to find a clear cut answer about whether or not you should > use hyperthreading on win2k server, but I haven't found one. Although I have > seen several references to this issue and seen posts of people saying to > shut if off. It seems win2k doesn't know the difference between logical and > physical processors, so maybe that's why it's not good for win2k. ? > > Does anyone know where I could find more info on this? We're going to turn > off hyperthreading on the webservers obviously because they perform better, > but I'm wondering if we will see performance gains by also shutting of > hyperthreading on the win2k SQL Servers. ? > > > Any insight into this would be great. > > Thanks. > >
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