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[Qemu-devel] Live Migration of a large guest : guest frozen on the desti

From: Chegu Vinod
Subject: [Qemu-devel] Live Migration of a large guest : guest frozen on the destination host
Date: Mon, 11 Jun 2012 07:02:06 -0700
User-agent: Mozilla/5.0 (Windows NT 5.1; rv:12.0) Gecko/20120428 Thunderbird/12.0.1


'am having some issues trying to live migrate a large guest and would like to get some pointers
on how to go about about debugging this. Here is some info. on the configuration

Hardware :
Two DL980's  each with 80 Westmere cores + 1 TB of RAM. Using a 10G NIC private link
(back to back) between two DL980's

Host software used:

Host 3.4.1 kernel
Qemu versions used :
  Case 1: upstream qemu  (1.1.50) - from qemu.git  
  Case 2 : 1.0.92 +  Juan Quintela's huge_memory changes

Guest :
40VCPUs + 512GB

Guest software used:
RHEL6.3 RC1  (had some basic boot issues with 3.4.1 kernel and udevd..)
Guest is booted off an FC LUN (visible to both the hosts).

[Note: 'am not using virsh/virt-manager etc. but just the qemu to start the guest and also interact with
the qemu monitor for live migration etc. Have set the migration speed to 10G but haven't changed the
downtime (default :  30ms) ]

Tried to live migrate this large guest..using either of the qemu's (i.e. Case 1 or Case2) and observed
the following :

When this guest was Idling  'was able to live migrate and have the guest come up fine on the
other host. Was able to interact with the guest on the destination host.

With workloads (e.g. AIM7-compute or SpecJBB or Google Stress App Test (SAT)) running in the
guest if we tried to do live migration.. we observe that [after a while] the source host claims that the
 live migration is complete...but the guest on the destination host is often in a "frozen/hung" state..
can't really interact with it or ping it.   Still trying to capture more information...but was also hoping to
get some clues/tips from the experts on these mailing lists...

[ BTW, is there a way to get a snap shot of the image of the guest on the source host just before
the "downtime" (i.e. start of stage 3) on the source host and compare that with the image of the guest on
the destination host just before its about to resume ? Is such a debugging feature already available ? ]


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