Bug 524970

Summary: Guest single-cpu IPI leads to a global IPI on host
Product: Red Hat Enterprise Linux 5 Reporter: Avi Kivity <avi>
Component: kvmAssignee: Eduardo Habkost <ehabkost>
Status: CLOSED ERRATA QA Contact: Lawrence Lim <llim>
Severity: medium Docs Contact:
Priority: medium    
Version: 5.5CC: knoel, ndai, riek, tools-bugs, virt-maint, ykaul
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Hardware: x86_64   
OS: Linux   
Whiteboard:
Fixed In Version: kvm-83-119.el5 Doc Type: Bug Fix
Doc Text:
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Clone Of: Environment:
Last Closed: 2010-03-30 07:54:36 UTC Type: ---
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description Flags
systemtap script to check for IPIs none

Description Avi Kivity 2009-09-22 20:03:56 UTC 
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).
Comment 7 Eduardo Habkost 2009-10-26 22:33:24 UTC 
Created attachment 366168 [details]
systemtap script to check for IPIs
Comment 13 errata-xmlrpc 2010-03-30 07:54:36 UTC 
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.

http://rhn.redhat.com/errata/RHSA-2010-0271.html