RHEL Engineering is moving the tracking of its product development work on RHEL 6 through RHEL 9 to Red Hat Jira (issues.redhat.com). If you're a Red Hat customer, please continue to file support cases via the Red Hat customer portal. If you're not, please head to the "RHEL project" in Red Hat Jira and file new tickets here. Individual Bugzilla bugs in the statuses "NEW", "ASSIGNED", and "POST" are being migrated throughout September 2023. Bugs of Red Hat partners with an assigned Engineering Partner Manager (EPM) are migrated in late September as per pre-agreed dates. Bugs against components "kernel", "kernel-rt", and "kpatch" are only migrated if still in "NEW" or "ASSIGNED". If you cannot log in to RH Jira, please consult article #7032570. That failing, please send an e-mail to the RH Jira admins at rh-issues@redhat.com to troubleshoot your issue as a user management inquiry. The email creates a ServiceNow ticket with Red Hat. Individual Bugzilla bugs that are migrated will be moved to status "CLOSED", resolution "MIGRATED", and set with "MigratedToJIRA" in "Keywords". The link to the successor Jira issue will be found under "Links", have a little "two-footprint" icon next to it, and direct you to the "RHEL project" in Red Hat Jira (issue links are of type "https://issues.redhat.com/browse/RHEL-XXXX", where "X" is a digit). This same link will be available in a blue banner at the top of the page informing you that that bug has been migrated.
Bug 601775 - libvirt: qemu: increase dd block size to speed up domain save
Summary: libvirt: qemu: increase dd block size to speed up domain save
Keywords:
Status: CLOSED CURRENTRELEASE
Alias: None
Product: Red Hat Enterprise Linux 6
Classification: Red Hat
Component: libvirt
Version: 6.0
Hardware: All
OS: Linux
low
medium
Target Milestone: rc
: ---
Assignee: Laine Stump
QA Contact: Virtualization Bugs
URL:
Whiteboard:
Depends On: 599091
Blocks:
TreeView+ depends on / blocked
 
Reported: 2010-06-08 15:20 UTC by Laine Stump
Modified: 2010-11-11 14:50 UTC (History)
10 users (show)

Fixed In Version: libvirt-0_8_1-10_el6
Doc Type: Bug Fix
Doc Text:
Clone Of: 599091
Environment:
Last Closed: 2010-11-11 14:50:32 UTC
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)

Description Laine Stump 2010-06-08 15:20:45 UTC 
+++ This bug was initially created as a clone of Bug #599091 +++

See https://bugs.launchpad.net/ubuntu/+source/qemu-kvm/+bug/524447/comments/5

Apparently increasing the dd block size greatly increases the speed of the domain save operation.

--- Additional comment from laine on 2010-06-07 13:56:00 EDT ---

commit 20206a4bc9f1293c69eca79290a55a5fa19976d5 in libvirt git changes the dd blocksize to 1M. This decreased the time required for a save of a suspended 512MB guest from 3min47sec to 56sec.
Comment 1 RHEL Program Management 2010-06-08 15:33:23 UTC 
This request was evaluated by Red Hat Product Management for inclusion in a Red
Hat Enterprise Linux major release.  Product Management has requested further
review of this request by Red Hat Engineering, for potential inclusion in a Red
Hat Enterprise Linux Major release.  This request is not yet committed for
inclusion.
Comment 3 Dave Allan 2010-06-24 01:35:53 UTC 
libvirt-0_8_1-10_el6 has been built in RHEL-6-candidate with the fix.

Dave
Comment 5 Osier Yang 2010-07-09 09:06:06 UTC 
libvirt-0.8.1-increase-dd-block-size.patch
libvirt-0.8.1-reduce-wasted-padding.patch

These two patches fix the problem.

[root@dhcp-66-65-* SOURCES]# rpm -q libvirt
libvirt-0.8.1-13.el6.x86_64
Comment 6 Daniel Berrangé 2010-08-25 16:47:16 UTC 
FYI: for people reading this ticket, there was actually an even more serious bug in QEMU itself. It would frequently sleep doing nothing due to small pipe buffer size, destroying performance. So for really fast domain save the QEMU fix is critical

commit 5e77aaa0d7d2f4ceaa4fcaf50f3a26d5150f34a6
Author: Avi Kivity <avi>
Date:   Wed Jul 7 19:44:22 2010 +0300

    QEMUFileBuffered: indicate that we're ready when the underlying file is ready
    
    QEMUFileBuffered stops writing when the underlying QEMUFile is not ready,
    and tells its producer so.  However, when the underlying QEMUFile becomes
    ready, it neglects to pass that information along, resulting in stoppage
    of all data until the next tick (a tenths of a second).
    
    Usually this doesn't matter, because most QEMUFiles used with QEMUFileBuffered
    are almost always ready, but in the case of exec: migration this is not true,
    due to the small pipe buffers used to connect to the target process.  The
    result is very slow migration.
Comment 7 wangyimiao 2010-09-10 02:00:04 UTC 
Verified this bug with RHEL6 RC build and it passed:
libvirt-0.8.1-27.el6.x86_64
qemu-img-0.12.1.2-2.113.el6.x86_64
qemu-kvm-0.12.1.2-2.113.el6.x86_64
kernel-2.6.32-71.el6.x86_64
Comment 8 releng-rhel@redhat.com 2010-11-11 14:50:32 UTC 
Red Hat Enterprise Linux 6.0 is now available and should resolve
the problem described in this bug report. This report is therefore being closed
with a resolution of CURRENTRELEASE. You may reopen this bug report if the
solution does not work for you.
Note You need to log in before you can comment on or make changes to this bug.