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):
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
Tons of IPIs everywhere
Tons of IPIs on just two cpus
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).
Created attachment 366168 [details]
systemtap script to check for IPIs
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on therefore solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.