Booting the Red Hat Enterprise Linux 5.4 or later operating system in a virtual machine reports APIC timer calibration warnings

Products

• VMware vSphere ESXi

Issue/Introduction

Symptoms:

• When booting the RedHat Enterprise Linux 5.4 or later operating system in a virtual machine, you see this warning:
  
  WARNING calibrate_APIC_clock: the APIC timer calibration may be wrong

Environment

VMware ESXi 3.5.x Embedded
VMware ESXi 4.0.x Embedded
VMware ESX 4.1.x
VMware ESXi 4.1.x Embedded
VMware ESXi 3.5.x Installable
VMware ESXi 4.1.x Installable
VMware ESX Server 3.5.x
VMware ESX 4.0.x
VMware ESXi 4.0.x Installable

Resolution

This warning does not impact the virtual machine and can be safely ignored.

This issue occurs if the maximum APIC timer calibration value is exceeded. By default, the APIC timer calibration value is set to 1000 cycles, which is not sufficient for virtual machines.

In a Red Hat Enterprise Linux 5.5 patch release, this value is increased to 5000 cycles, which eliminates the warning on most systems. However, the warning may still be visible on ESX hosts using AMD Opteron processors.

This issue is present in kernels as new as 2.6.18-274.el5, however there is currently a bug report open with Red Hat to increase the value to 10000 when running in a virtual machine. This can be publicly viewed at https://bugzilla.redhat.com/show_bug.cgi?id=743368.

As a workaround, to remove this warning, you can manually modify the APIC timer calibration value for the guest operating system by setting this boot option:

apiccalibrationdiff=10000