Quoting Linus Torvalds [off-list ref]:

quoted

Here's the status with -rc3: better, but still does not work as well as 2.6.20.

Ok. I think we mostly solved the irq-related stuff, but you might want to 
check whether you have CONFIG_NOHZ on or off and whether that makes a 
difference.

This testing was done without NO_HZ.

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MST