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Re: [PATCH v16 QEMU 00/16] Add migration support for VFIO devices

From: Alex Williamson
Subject: Re: [PATCH v16 QEMU 00/16] Add migration support for VFIO devices
Date: Tue, 31 Mar 2020 12:34:24 -0600

On Wed, 25 Mar 2020 02:38:58 +0530
Kirti Wankhede <address@hidden> wrote:

> Hi,
> This Patch set adds migration support for VFIO devices in QEMU.

Hi Kirti,

Do you have any migration data you can share to show that this solution
is viable and useful?  I was chatting with Dave Gilbert and there still
seems to be a concern that we actually have a real-world practical
solution.  We know this is inefficient with QEMU today, vendor pinned
memory will get copied multiple times if we're lucky.  If we're not
lucky we may be copying all of guest RAM repeatedly.  There are known
inefficiencies with vIOMMU, etc.  QEMU could learn new heuristics to
account for some of this and we could potentially report different
bitmaps in different phases through vfio, but let's make sure that
there are useful cases enabled by this first implementation.

With a reasonably sized VM, running a reasonable graphics demo or
workload, can we achieve reasonably live migration?  What kind of
downtime do we achieve and what is the working set size of the pinned
memory?  Intel folks, if you've been able to port to this or similar
code base, please report your results as well, open source consumers
are arguably even more important.  Thanks,


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