question on PV pass-through patch

question on PV pass-through patch

[Masroor Vettuparambil]

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Hi all,
 
I could see some patches are submitted to support PV domain pass-through
hotplug.
So my question is, if we pci-detach all pci devices from domU, then can
we able to migrate such a domain?
 
regards,
Masroor

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Re: question on PV pass-through patch

[Yosuke Iwamatsu]

Hi,

Masroor Vettuparambil wrote:
> I could see some patches are submitted to support PV domain pass-through 
> hotplug.
> So my question is, if we pci-detach all pci devices from domU, then can 
> we able to migrate such a domain?

Yes, we can.
And I think it is one of the important features of pci
pass-throughn hotplug.

Regards,
-------------------
Yosuke Iwamatsu
         NEC Corporation

RE: question on PV pass-through patch

[Masroor Vettuparambil]

 
I tried your patch with CONFIG_XEN_PCIDEV_BACKEND_VPCI.
Detached the pci on the source and attached another slot to migrated
domU on destination. 
Migration is happening smoothly. thanks for your work.

a minor thing I noticed is, dmesg on domU shows the following warning
during pci-detach,
WARNING: g.e. still in use!
WARNING: leaking g.e. and page still in use!

I wonder if we can achieve a 'live' migration of direct access, ie,
without interrupting the network traffic?
Something like creating a vif(network-attach) on domU for carrying the
n/w traffic temporarily till the migration is over.
After migration, move the n/w traffic back from vif to newly
pci-attached NIC on the destination.
Any thought?

regards,
Masroor

-----Original Message-----
From: Yosuke Iwamatsu [mailto:y-iwamatsu@ab.jp.nec.com] 
Sent: Monday, March 10, 2008 7:07 AM
To: Masroor Vettuparambil
Cc: xen-devel@lists.xensource.com
Subject: Re: [Xen-devel] question on PV pass-through patch

Hi,

Masroor Vettuparambil wrote:
> I could see some patches are submitted to support PV domain 
> pass-through hotplug.
> So my question is, if we pci-detach all pci devices from domU, then 
> can we able to migrate such a domain?

Yes, we can.
And I think it is one of the important features of pci pass-throughn
hotplug.

Regards,
-------------------
Yosuke Iwamatsu
         NEC Corporation

Re: question on PV pass-through patch

[Yosuke Iwamatsu]

Masroor Vettuparambil wrote:
>  
> I tried your patch with CONFIG_XEN_PCIDEV_BACKEND_VPCI.
> Detached the pci on the source and attached another slot to migrated
> domU on destination. 
> Migration is happening smoothly. thanks for your work.
> 
> a minor thing I noticed is, dmesg on domU shows the following warning
> during pci-detach,
> WARNING: g.e. still in use!
> WARNING: leaking g.e. and page still in use!

I'm not sure what this means, but it looks like something is wrong
with the disconnect procedure of pcifront/pciback.

> I wonder if we can achieve a 'live' migration of direct access, ie,
> without interrupting the network traffic?
> Something like creating a vif(network-attach) on domU for carrying the
> n/w traffic temporarily till the migration is over.
> After migration, move the n/w traffic back from vif to newly
> pci-attached NIC on the destination.
> Any thought?

Actually I've been thinking of "passthrough domain live migration"
using a multipath-driver which combines a passthrough device and
a virtual device. Below is an idea of live migrating a domU
which has passthrough network device attached.

- First create bond0 and add the passthrough interface to it.
- Usually we use the passthrough interface (fast path).
- Before migration, attach a vif to the domU and add the vif interface
   to bond0. Then remove the passthrough inteface from bond0 and do
   pci-detach. We can migrate without network disconnection because
   the vif is now enabled (slow path).
- After migration, do pci-attach, add passthrough interface to bond0,
   and disconnect the vif interface (switch back to fast path).

I hope this method works, but I haven't have an opportunity to try it
myself yet.

Thanks,
-------------------
Yosuke Iwamatsu
     NEC Corporation