Soft lockup messages from Linux kernel running in an SMP-enabled virtual machine

Products

• VMware vSphere ESXi

Issue/Introduction

When running a Linux kernel in a symmetric multiprocessing (SMP) enabled virtual machine, messages similar to BUG: soft lockup detected on CPU#1! are written to the message log file. The exact format of these messages vary from kernel to kernel, and might be accompanied by a kernel stack backtrace.

 

Many Linux kernels have a soft lockup watchdog thread, and report soft lockup messages if that watchdog thread does not get scheduled for more than 10 seconds. On a physical host, a soft lockup message generally indicates a kernel bug or hardware bug. When running in a virtual machine, this might instead indicate high levels of overcommitment (especially memory overcommitment) or other virtualization overheads.

Environment

VMware vSphere ESXi

Resolution

The soft lockup messages are not kernel panics, and generally appears when the virtual machine is using a large amount of its resources.

 

To stop the error messages from appearing as frequently:

Some kernels allow you to adjust the soft lockup threshold by running the command:

echo time > /proc/sys/kernel/softlockup_thresh

Where time is the number of seconds after which a soft lockup is reported. The default is generally 10 seconds.

Note: Depending on your Linux kernel version, the command to adjust the soft lockup threshold may be different, consult your vendor documentation.