Description of problem:

When a guest issues an IPI (or when kvm needs to signal another processor for another reason), all host processors are interrupted, not just the ones requested by the guest or kvm.  This leads to increased host load and wastes resources.

Version-Release number of selected component (if applicable):
kvm-83-105.el5

How reproducible:
Always

Steps to Reproduce:
1. Start a 2-vcpu guest on a larger host
2. Run an IPI-intensive workload (pipetest with processes pinned to vcpus) 
3. watch /proc/interrupts
  
Actual results:
Tons of IPIs everywhere

Expected results:
Tons of IPIs on just two cpus

Additional info:

Cause: kvm's smp_call_function_single() is translated to 2.6.18's smp_call_function() instead of smp_call_function_single() (since it used not to be exported).