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Re: Guest OS becomes totally unresponsive when running on VMware

From: Alex Bennée
Subject: Re: Guest OS becomes totally unresponsive when running on VMware
Date: Thu, 18 Feb 2021 11:53:27 +0000
User-agent: mu4e 1.5.8; emacs 28.0.50

Salvatore Mazzarino <apocalipse89@gmail.com> writes:

> I'm running QEMU v4.2.0 inside a Docker container. The Docker container runs 
> on a VMware VM running Flatcar Linux OS with kernel version 5.4.92. It 
> happens that the QEMU process starts to show up an high usage of CPU. The 
> CPUs that the Qemu process uses go into saturation and the guest OS running 
> by QEMU becomes totally unresponsive. Note that this issue does not occur 
> when QEMU runs on a bare metal machine. It only happens when we have nested 
> virtualization. 
> I would like to debug the QEMU process to get where it get stuck. Then I 
> compiled a version with tracing enabled. Following the tracing doc I was able 
> to get traces of QEMU. 
> Problem here is that I'm not sure exactly what function to trace. If I
> trace all the file is huge. In 5 seconds of tracing in fact I get over
> 2GB. I would need some guidance to narrow down the issue finding the
> right QEMU trace to get some useful info. Which function would you
> recommend to trace?

Tracing is best used when tracking down very specific performance issues
- as you have found it can very quickly saturate logs.

Does perf top point you towards any areas where QEMU is particularly
busy? Have you compared the perf report of a in-container vs out of
container QEMU?

Alex Bennée

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