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Re: [Qemu-devel] [RFC v2 0/2] Add live migration support in the PVRDMA d

From: Marcel Apfelbaum
Subject: Re: [Qemu-devel] [RFC v2 0/2] Add live migration support in the PVRDMA device
Date: Sat, 6 Jul 2019 22:04:55 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1

Hi Sukrit,

On 7/6/19 7:09 AM, Sukrit Bhatnagar wrote:
Changes in v2:

* Modify load_dsr() such that dsr mapping is not performed if dsr value
   is non-NULL. Also move free_dsr() out of load_dsr() and call it right
   before if needed. These two changes will allow us to call load_dsr()
   even when we have already done dsr mapping and would like to go on
   with the rest of mappings.

* Use VMStateDescription instead of SaveVMHandlers to describe migration
   state. Also add fields for parent PCI object and MSIX.

* Use a temporary structure (struct PVRDMAMigTmp) to hold some fields
   during migration. These fields, such as cmd_slot_dma and resp_slot_dma
   inside dsr, do not fit into VMSTATE macros as their container
   (dsr_info->dsr) will not be ready until it is mapped on the dest.

* Perform mappings to CQ and event notification rings after the state is
   loaded. This is an extension to the mappings performed in v1;
   following the flow of load_dsr(). All the mappings are succesfully
   done on the dest on state load.


Link(s) to v1:

Things working now (were not working at the time of v1):

* vmxnet3 is migrating successfully. The issue was in the migration of
   its PCI configuration space, and is solved by the patch Marcel had sent:

* There is no problem due to BounceBuffers which were failing the dma mapping
   calls in state load logic earlier. Not sure exactly how it went away. I am
   guessing that adding the PCI and MSIX state to migration solved the issue.

I am sure it was connected somehow, anyway, I am glad we can continue
with the project.

What is still needed:

* A workaround to get libvirt to support same-host migration. Since
   the problems faced in v1 (mentioned above) are out of the way, we
   can move further, and in doing so, we will need this.

[Adding Daniel  and Michal]
Is there anyway to test live-migration for libvirt domains on the same host?
Even a 'hack' would be enough.

Sukrit, another way you could do it is by enabling nested virtualization
and have 2 Vms as hosts. I suppose the migration will take some time though...


Sukrit Bhatnagar (2):
   hw/pvrdma: make DSR mapping idempotent in load_dsr()
   hw/pvrdma: add live migration support

  hw/rdma/vmw/pvrdma_main.c | 104 +++++++++++++++++++++++++++++++++++---
  1 file changed, 96 insertions(+), 8 deletions(-)

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