Minaz (2/6/2014)
We took out expensive queries and that was tunes and used a new sql plan. But after 3 hours same query became once again the expensive one.
How was performance after you tuned the query? Did the CPU drop? Also, what do you mean "used a new sql plan"? Did you provide it a Plan Guide?
It sounds like the expensive queries need to have another round of performance enhancements. If you are having issues with improving performance on the expensive queries post them here and someone should be able to help you with them.
I was refering and assuming if this is bug with CPU spin lock.
I wouldn't think there was an issue with the spin locks. I would first try to improve the queries you mentioned first and rule that out.