Re: Virtio Drivers on Dragonfly

["Samuel J. Greear" <sjg@xxxxxxxxxxxx>]

>>
>> I thought that after being on a track with virtio drivers, I will go with doing
>> some work on check pointing vkernel. After that we can move forward with vkernel
>> migration using opportunistic replay approach as we have the checkpoints
>> generated. But all this depends on your guidance, I can go the way you guys
>> suggest.
>
> Actually, I have asked Matt about vkernel checkpointing recently as I
> have huge interest in being able to suspend to disk or migrate vkernels
> to other machines. I thought that one had to modify the kernel to
> support checkpointing of multiple vmspaces (which the vkernel makes use
> of), and which is currently not supported (actually doesn't sound too
> complicated), but Matt said that it should be possible to do without any
> modification of the real kernel. One would have to teach the vkernel to
> catch the SIGCKPT and to collect and save the vpagetable information for
> the vkernel-processes together with configuration information like
> network device and console, and to restore it upon SIGTHAW.
>
> I might take a stab at it after my exam on Monday.
>
> Being able to checkpoint vkernels would enable us to migrate a running
> vkernel within a few seconds to another box, e.g. for the purpose of
> CPU/network load-balancing, or to save energy by employing VaryOn/Off
> strategies, i.e. shutting down servers with too little load. The whole
> consolidation/virtualization buzz would find it's way into
> DragonFly :).
>
> Another great application of vkernels could be for laptops. Imagine your
> laptop runs on DragonFly, and your host kernel is running a X11 display
> server, while all your X11 clients run inside the vkernel. This enables
> you to checkpoint the vkernel, shut down the laptop, and to later
> restore where you left off (assuming X11 doesn't keep state on the
> X11-server).
>
> I also think that vkernel checkpointing is a great feature for virtual
> hosting. Especially combined with swapcache, one could run a huge number
> of vkernels on a single machine, giving each enough main memory, backed
> by a SSD. Whether it performs well is another question :)
>
> Regards,
>
>  Michael
>
>

There is another component to this, we currently can't checkpoint any
threaded program because we do not save and restore the segment
registers, which is how TLS is implemented. I started on this (dirty)
http://gitweb.dragonflybsd.org/~sjg/dragonfly.git/commitdiff/e29b6f2d0c961889b55e94ce7ac6aa0e398d7071
but its really a bit beyond me.

Sam