Re: [Qemu-devel] live migration vs device assignment (motivation)

[Alexander Duyck]

On Wed, Dec 9, 2015 at 8:26 AM, Lan, Tianyu <address@hidden> wrote:

> For other kind of devices, it's hard to work.
> We are also adding migration support for QAT(QuickAssist Technology) device.
>
> QAT device user case introduction.
> Server, networking, big data, and storage applications use QuickAssist
> Technology to offload servers from handling compute-intensive operations,
> such as:
> 1) Symmetric cryptography functions including cipher operations and
> authentication operations
> 2) Public key functions including RSA, Diffie-Hellman, and elliptic curve
> cryptography
> 3) Compression and decompression functions including DEFLATE and LZS
>
> PCI hotplug will not work for such devices during migration and these
> operations will fail when unplug device.

I assume the problem is that with a PCI hotplug event you are losing
the state information for the device, do I have that right?

Looking over the QAT drivers it doesn't seem like any of them support
the suspend/resume PM calls.  I would imagine it makes it difficult
for a system with a QAT card in it to be able to drop the system to a
low power state.  You might want to try enabling suspend/resume
support for the devices on bare metal before you attempt to take on
migration as it would provide you with a good testing framework to see
what needs to be saved/restored within the device and in what order
before you attempt to do the same while migrating from one system to
another.

- Alex