What is __kernel_vsyscall?

Question

I got a core that looks very different from the ones I usually get - most of the threads are in __kernel_vsyscall() :

  9 process 11334  0xffffe410 in __kern         


        

Answer 1

As Adam said, the main reason is performance. See this link for some old numbers http://lkml.org/lkml/2002/12/9/13.

If you have a vDSO enabled kernel, you're not using interrupts to run syscalls, as Stefan said, actually was because interrupts was getting slower that the whole vDSO thing was added to the kernel.