twin CPUs behaving oddly..or are they? | SQL Server Performance Forums

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twin CPUs behaving oddly..or are they?

Iw as watching a twin CPU machine ( well its a single CPU machine with hyperthreading ) and I noticed the CPU level was averaging 50%. But, when I looked closely the first CPU was acting like a mirror of the second CPU if you drew an imaginary line at 50% on the graph…such that when one CPU was say at 70% ( i.e. 50% + 20% ) the other CPU would be at 30% ( 50% – 20% ). Is this normal for multi CPU machines and if so, why? I also came across this article :
…which says that one CPU can be locked at 100% while the others are running at 0% because there was only one data file in the file group for the database. Any thoughts? Thnaks,

SQL Server will automatically use all CPU available. On the server properties page make sure that all CPU’s are checked. It is better to have your logs on Raid 1 as the transaction log is written sequentially. You may want to test tempdb performance on either array, but I would suspect it would be better on RAID5 as that has higher write performance. For small databases (less than 50 gig) there is no performance gain to be made if the data/log files are on the same drive/raid array. However, Microsoft have done some tests with the Human Genome project that suggests that some gains can be made for VLDBs > 1Tb. See link.
Satya SKJ
This posting is provided “AS IS” with no rights for the sake of knowledge sharing.
it depends what you are doing, keep in mind that there is work being done by your own thread/spid (which normally uses 1 thread, but could use more, parallel plans)
however, if you are inserting data, the log writer has work to do etc, check the activity of the lower spids 1-50 are system spids,
so it sounds like 1 processor is handling work from a user spid, and the other processor is handling associated work from a system spid,
then periodically, the processors are switched,
could be other things too, no reason to worry