Bug 699674 - decrease migration_downtime cause migrtion speed very slow
Summary: decrease migration_downtime cause migrtion speed very slow
Keywords:
Status: CLOSED NOTABUG
Alias: None
Product: Red Hat Enterprise Linux 5
Classification: Red Hat
Component: kvm
Version: 5.7
Hardware: x86_64
OS: Linux
high
high
Target Milestone: rc
: ---
Assignee: Virtualization Maintenance
QA Contact: Virtualization Bugs
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2011-04-26 10:39 UTC by Mike Cao
Modified: 2011-05-10 11:05 UTC (History)
6 users (show)

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Clone Of:
Environment:
Last Closed: 2011-05-10 11:05:26 UTC
Target Upstream Version:

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Description Mike Cao 2011-04-26 10:39:02 UTC 
Description of problem:


Version-Release number of selected component (if applicable):
# uname -r
2.6.18-256.el5
# rpm -q kvm
kvm-83-231.el5


How reproducible:
100%

Steps to Reproduce:
1.start VM in src host
CLI:/usr/libexec/qemu-kvm -rtc-td-hack -usbdevice tablet -no-hpet -drive file=win7-32.qcow2,if=ide,werror=stop,cache=none,format=qcow2,media=disk -cpu qemu64,+sse2 -smp 16,cores=16 -m 4G -net nic,macaddr=00:12:24:5f:a6:99,model=virtio,vlan=0 -net tap,script=/etc/qemu-ifup,vlan=0  -uuid `uuidgen` -vnc :1 -boot c  -balloon none -monitor stdio
2.start lisetnning port
3.set migration downtime to 0.00000001s
(qemu)migrate_set_downtime 0.00000001
4(qemu)migrate -d tcp:0:5888
5.check migration speed  
Actual results:
20kb/s

Expected results:
set migration dowmtime should not influence migration speed. it should keep 30MB/s

Additional info:
Comment 1 FuXiangChun 2011-05-10 10:55:05 UTC 
reporduced on
uname -r
2.6.18-260.el5
rpm -qa|grep kvm
kvm-83-232.el5
Comment 2 juzhang 2011-05-10 11:05:26 UTC 
Close this bug according to bz699952 comment2,if need further investigation,please re-open this issue.

--snip of comment2---
Migration downtime affects migration speed because qemu has more work to do
between iterations (checking the dirty bitmap, etc.).  Besides, a downtime of
10^-10 seconds makes little sense when a clock cycle is three times that.
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