RE: [Qemu-devel] [RFC kernel 0/2]A PV solution for KVM live migration optimization

On 3/8/2016 4:44 PM, Amit Shah wrote:

quoted

On (Fri) 04 Mar 2016 [15:02:47], Jitendra Kolhe wrote:

quoted

quoted

quoted

* Liang Li (liang.z.li@intel.com) wrote:

quoted

The current QEMU live migration implementation mark the all the
guest's RAM pages as dirtied in the ram bulk stage, all these
pages will be processed and that takes quit a lot of CPU cycles.

From guest's point of view, it doesn't care about the content in
free pages. We can make use of this fact and skip processing the
free pages in the ram bulk stage, it can save a lot CPU cycles and
reduce the network traffic significantly while speed up the live
migration process obviously.

This patch set is the QEMU side implementation.

The virtio-balloon is extended so that QEMU can get the free pages
information from the guest through virtio.

After getting the free pages information (a bitmap), QEMU can use
it to filter out the guest's free pages in the ram bulk stage.
This make the live migration process much more efficient.

Hi,
  An interesting solution; I know a few different people have been
looking at how to speed up ballooned VM migration.

Ooh, different solutions for the same purpose, and both based on the

balloon.

quoted

quoted

We were also tying to address similar problem, without actually
needing to modify the guest driver. Please find patch details under mail

with subject.

quoted

quoted

migration: skip sending ram pages released by virtio-balloon driver

The scope of this patch series seems to be wider: don't send free
pages to a dest at all, vs. don't send pages that are ballooned out.

		Amit

Hi,

Thanks for your response. The scope of this patch series doesn’t seem to
take care of ballooned out pages. To balloon out a guest ram page the guest
balloon driver does a alloc_page() and then return the guest pfn to Qemu, so
ballooned out pages will not be seen as free ram pages by the guest.
Thus we will still end up scanning (for zero page) for ballooned out pages
during migration. It would be ideal if we could have both solutions.

Agree,  for users who care about the performance, just skipping the free pages.
For users who have already turned on virtio-balloon,  your solution can take effect.

Liang

Thanks,
- Jitendra

_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization