Wierd context-switching issue on Xeon

Folks,

We're seeing some odd issues with hyperthreading-capable Xeons, whether or not 
hyperthreading is enabled.   Basically, when a small number of really-heavy 
duty queries hit the system and push all of the CPUs to more than 70% used 
(about 1/2 user & 1/2 kernel), the system goes to 100,000+ context switcthes 
per second and performance degrades.  

I know that there's other Xeon users on this list ... has anyone else seen 
anything like that?   The machines are Dells running Red Hat 7.3.

-- 
-Josh Berkus
 Aglio Database Solutions
 San Francisco