Bug 1686321

Fangge:
  Can you please describe:
     a) The guest that you're running including the size of the VM (in GB RAM), the program it's running
     b) How you're triggering the postcopy switchover
     c) The network connection between the hosts
     d) how long the postcopy phase is?
     e) Which is the source and destination host machines you're using?

(In reply to Dr. David Alan Gilbert from comment #1)
> Fangge:
>   Can you please describe:
>      a) The guest that you're running including the size of the VM (in GB
> RAM), the program it's running
The size of the VM is 1048576 KiB, I run stress in VM: # stress --cpu 8 --io 4 --vm 4 --vm-bytes 128M

>      b) How you're triggering the postcopy switchover
I use virsh command: virsh migrate-postcopy $guest, it will call QMP: migrate-start-postcopy

>      c) The network connection between the hosts
The maximum network speed is 1000Mb/s. The NICs info is as below:
Src: 2: eno1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    link/ether 14:58:d0:d3:31:ab brd ff:ff:ff:ff:ff:ff
    inet 10.16.184.37/22 brd 10.16.187.255 scope global dynamic noprefixroute eno1
       valid_lft 73170sec preferred_lft 73170sec

Dest:2: eno1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    link/ether a0:2b:b8:31:26:a4 brd ff:ff:ff:ff:ff:ff
    inet 10.16.65.242/21 brd 10.16.71.255 scope global dynamic noprefixroute eno1
       valid_lft 73352sec preferred_lft 73352sec


>      d) how long the postcopy phase is?
I didn't pay attention to the time. But total migration time is:
# virsh domjobinfo avocado-vt-vm1  --completed
Job type:         Completed   
Operation:        Outgoing migration
Time elapsed:     72105        ms         ==> total time
Time elapsed w/o network: 72097        ms
Data processed:   3.133 GiB
Data remaining:   0.000 B
Data total:       1.005 GiB
Memory processed: 3.133 GiB
Memory remaining: 0.000 B
Memory total:     1.005 GiB
Memory bandwidth: 44.819 MiB/s
Dirty rate:       0            pages/s
Page size:        4096         bytes
Iteration:        7           
Postcopy requests: 594         
Constant pages:   48095       
Normal pages:     819479      
Normal data:      3.126 GiB
Total downtime:   275          ms
Downtime w/o network: 267          ms
Setup time:       28           ms

The post-copy phase may be around (72105-14139=57966)ms, which is not so accurate.

>      e) Which is the source and destination host machines you're using?
Src: hp-dl120gen9-01.khw.lab.eng.bos.redhat.com
Dest: hp-ml150gen9-01.rhts.eng.bos.redhat.com

I've checked with the code, the postcopy bandwidth setting is only read at the point of switchover from precopy to postcopy.
Yes we can fix that to allow it to be changed.

Need to fix migrate_params_apply to not call qemu_file_set_rate_limit for max_bandwidth if pc is active, but to call it in the code for max_postcopy_bandwdith case.

Posted upstream:
   migration/postcopy: Update the bandwidth during postcopy

Merged upstream as c38c1c142e64901b09f5 it'll be in qemu 4.0

Hi, all
I verify this bz in environment[1], test steps are like polarion case RHEL-150076[2], the issue is gone.

environment[1]
src and dst host info: kernel-modules-4.18.0-95.el8.x86_64 & qemu-img-4.0.0-3.module+el8.1.0+3265+26c4ed71.x86_64
guest info: kernel-4.18.0-100.el8.x86_64

polarion case[2]:
https://polarion.engineering.redhat.com/polarion/#/project/RedHatEnterpriseLinux7/workitem?id=RHEL-150076


Best regards,
Li Xiaohui

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/RHBA-2019:3723