Bug 1269713

Summary:	The difference setting xml place of virtio and scsi ioeventfd disk should be descript more clearly
Product:	Red Hat Enterprise Linux 7	Reporter:	Xuesong Zhang <xuzhang>
Component:	doc-Virtualization_Deployment_and_Administration_Guide	Assignee:	Jiri Herrmann <jherrman>
Status:	CLOSED CURRENTRELEASE	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	7.2	CC:	dyuan, mkletzan, mzhan, pzhang, xuzhang
Target Milestone:	rc	Keywords:	Documentation
Target Release:	---
Hardware:	Unspecified
OS:	Unspecified
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Fixed In Version:		Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2016-11-07 14:49:45 UTC	Type:	Bug
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description Xuesong Zhang 2015-10-08 03:34:47 UTC

Document URL:
26.18.1.6. Driver element
http://documentation-devel.engineering.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Virtualization_Deployment_and_Administration_Guide/sect-Manipulating_the_domain_xml-Devices.html#sect-Devices-Hard_drives_floppy_disks_CDROMs

26.18.4 . Controllers
http://documentation-devel.engineering.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Virtualization_Deployment_and_Administration_Guide/sect-Manipulating_the_domain_xml-Devices.html#sect-Devices-Controllers

Section Number and Name:

Describe the issue:
As you can see in the following libvirt.org, there is one new optional element "ioeventfd" for the scsi controller.
http://libvirt.org/formatdomain.html#elementsControllers
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ioeventfd
The optional ioeventfd attribute specifies whether the controller should use I/O asynchronous handling or not. Accepted values are "on" and "off". Since 1.2.18
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There is another ioeventfd element in disk xml section, following is for you reference.
http://libvirt.org/formatdomain.html#elementsDisks
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The optional ioeventfd attribute allows users to set domain I/O asynchronous handling for disk device. The default is left to the discretion of the hypervisor. Accepted values are "on" and "off". Enabling this allows qemu to execute VM while a separate thread handles I/O. Typically guests experiencing high system CPU utilization during I/O will benefit from this. On the other hand, on overloaded host it could increase guest I/O latency. Since 0.9.3 (QEMU and KVM only) In general you should leave this option alone, unless you are very certain you know what you are doing
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They are all allow users to set domain I/O asynchronous handling for disk device. The difference is the "ioeventfd" attribute in <disk...> xml section is for the virtio disk, the "ioeventfd" attribute in <controller type='scsi'...> xml section is for the scsi disk. Please highlight the difference in the administrator guide, otherwise the cumstomer will be confused.

Suggestions for improvement:

Additional information: