Bug 1484234

Summary:	suggested to document that tx_queue_size in interface section only support 256 for interface types other than vhostuser
Product:	Red Hat Enterprise Linux 7	Reporter:	yalzhang <yalzhang>
Component:	libvirt	Assignee:	Michal Privoznik <mprivozn>
Status:	CLOSED ERRATA	QA Contact:	yalzhang <yalzhang>
Severity:	unspecified	Docs Contact:
Priority:	unspecified
Version:	7.4	CC:	chhu, jishao, rbalakri, xuzhang
Target Milestone:	rc	Keywords:	Upstream
Target Release:	---
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:	libvirt-3.7.0-1.el7	Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2018-04-10 10:55:31 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 yalzhang@redhat.com 2017-08-23 05:59:02 UTC

Description of problem:
The tx_queue_size is supported on libvirt libvirt-3.2.0-14.el7_4.3.x86_64, while 
set tx_queue_size to 1024 or 512 in interfaces other than vhostuser interface type makes no changes, the tx_queue size on guest will always keep as 256.

Suggested to document it somewhere like in /usr/share/doc/libvirt-docs-3.2.0/html/formatdomain.html#elementsDriverBackendOptions

Version-Release number of selected component (if applicable):
libvirt-docs-3.2.0-14.el7_4.3.x86_64

How reproducible:

Steps to Reproduce:
1.
2.
3.

Actual results:

Expected results:


Additional info:
Refer to https://bugzilla.redhat.com/show_bug.cgi?id=1482514#c14, "for vhost-user, we allow tx queue size to be greater than 256, for vhost-kernel, we don't allow more than 256." this is kernel limitation.

Comment 2 Michal Privoznik 2017-08-29 15:11:32 UTC

Patch proposed upstream:

https://www.redhat.com/archives/libvir-list/2017-August/msg00914.html

Comment 3 Michal Privoznik 2017-08-31 07:57:27 UTC

I've pushed the patch upstream:

commit b39464ba26424053ec5fd953c89087eb66d56d73
Author:     Michal Privoznik <mprivozn>
AuthorDate: Tue Aug 29 17:01:16 2017 +0200
Commit:     Michal Privoznik <mprivozn>
CommitDate: Wed Aug 30 08:49:48 2017 +0200

    docs: Document yet another limitation of tx_queue_size
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1484234
    
    Turns out, only vhostuser type of interfaces are supported
    currently.
    
    Signed-off-by: Michal Privoznik <mprivozn>

v3.7.0-rc1-4-gb39464ba2

Comment 5 yalzhang@redhat.com 2017-09-07 06:43:10 UTC

checked on file:///usr/share/doc/libvirt-docs-3.7.0/html/formatdomain.html
It is documented:

"Moreover, some hypervisors may pose some restrictions on actual value. For instance, QEMU v2.9 requires value to be a power of two from [256, 1024] range. In addition to that, this may work only for a subset of interface types, e.g. aforementioned QEMU enables this option only for vhostuser type. Since 3.7.0 (QEMU and KVM only)"

Comment 9 errata-xmlrpc 2018-04-10 10:55:31 UTC

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHEA-2018:0704