Improved reboot and shutdown time
Reboot time is improved for KVM guests running in IBM Secure Execution mode.
Improved reboot time
A feature of QEMU that allows guests to reboot quickly is available by default.
On the KVM host, the file /sys/module/kvm/parameters/async_destroy indicates whether the feature is active.
Enabling shutdown time improvement
To enable shutdown improvement, add the async_teardown element to the guest's XML.
Secure execution mode requires that a guest’s memory be securely cleared during shutdown. This process can slow down the shutdown if it’s done synchronously. To mitigate this delay, you can enable the async-teardown option, which allows the shutdown process to complete asynchronously.
When using async-teardown, ensure the host has sufficient free memory before
launching any new guest. Shutting down an IBM Secure Execution guest with
async-teardown clears the memory asynchronously, which can lead to
out-of-memory situations, particularly with large guests. To further mitigate these risks, avoid
using memory allocation mode immediate
.
Confirming support for async-teardown
# virsh domcapabilities | grep async-tear <async-teardown supported='yes'/>
Configuring async-teardown
<domain type='kvm'>
<name>fast-shutdown</name>
...
<memory unit='KiB'>1150976</memory>
<vcpu placement='static'>2</vcpu>
<os>
<type arch='s390x' machine='s390-ccw-virtio'>hvm</type>
</os>
<features>
<async-teardown enabled='yes'/>
</features>
<devices>
<emulator>/usr/bin/qemu-system-s390x</emulator>
...
</devices>
</domain>For details about setting up features for and operating Linux on KVM instances, see KVM Virtual Server Management, SC34-2752.
The following is to be removed when the VSM book is available.