[Xen-devel] Re: Experience, and questions in using Xen 1.2 with new control tool

[Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>]

------- Forwarded Message

To: "Yan-Ching CHU" <cs0u210a@xxxxxxxxxxxxxxx>
cc: xen-devel-admin@xxxxxxxxxxxxxxxxxxxxx,
    "Ian Pratt" <Ian.Pratt@xxxxxxxxxxxx>, Ian.Pratt@xxxxxxxxxxxx
Subject: Re: Experience, and questions in using Xen 1.2 with new control tool 
In-reply-to: Your message of "Tue, 03 Feb 2004 04:34:04 GMT."
             <020e01c3ea0e$f458ae00$0100a8c0@barcelona> 
Date: Tue, 03 Feb 2004 09:00:27 +0000
From: Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>
Message-Id: <E1AnwQ0-0007DK-00@xxxxxxxxxxxxxxxxxxxx>


>     'Great work!' to The Xen team. In general I think the hypervisor is much 
> more stable and the control tool is much more coherent and centralized in 
> v1.2.

Thanks!

>     1) After starting new domain I can only ssh to it by 'ssh 
> root@xxxxxxxxxxx' but not as what in the README.CD of Xen 1.2 (and earlier) 
> says to ssh with port number 2200 + domain_id, if so I would get connection 
> refused. I have started 'xen_nat_enable' am I setting anything wrong or 
> missing anything? Or just leave it?

That's a documentation bug coupled with a slight 'democd' config
file bug.

There's nothing special about 169.254.x.x addresses other than
theu never go on the LAN. 

You can assign a new VM any arbitrary IP address (though it
should be unique!) and then be able to ssh into it from domain 0.

If you run the xen_nat_enable script, some port forwarding rules
are inserted to enable you to access the new domain from other
machines on your LAN (assuming domain 0 has a LAN address as well
as 169.254.1.0, which it gets by convention).

The port forwarding rules arrange to route port 2200+x on
domain0's IP to 169.254.1.x port 22 (for 1 < x < 20).

If you've assigned a domain a link local IP that's in this range
it should get the packets. 

The README needs to make this clearer.

 
>     2) 'xc destroy' is so powerful that it can kill Domain 0 directly without 
> even a checking or a prompt, if the admin (likely be root) accidentally key 
> in 0 and enter without serious checking this may cause troubles.

Functioning as per specification ;-)

We could change it if people prefer.

>     3) I am using 256MB in my laptop running 128MB for domain 0, but I can't 
> use up the rest of the memory for other domains. Is there any upper bound? By 
> the way I have tried running a domain by just using 8MB memory and ssh it 
> successfully. (2MB is not enough for kernel and 4MB with applications 
> complaining not enough pages) And one more is that if there is not enough 
> memory the return message will be 'error creating domain', it would be useful 
> if it can point to something related to memory.

The amount of memory 'eaten' by Xen is basically a constant plus
some amount proportional to the amount of memory in the machine.
It's fair to say that we haven't gone out of our way to minimize
the memory overhead (so far), as all our machines have plenty of
memory. We certainly reserve more for Xen's heap etc than is
probably sane.

The error message is terrible -- we'll fix this. The dom0 op
returns ENOMEM, but we seem to throw the useful return code away
somewhere at present...
 
>     4) I am not sure if the suspend/restore function is ready. But I have 
> tried Create->Stop->Save a domain and Restore->Start it again. The network 
> interface and sshd seem totally down after restore, if the sshd is down seems 
> there is no way to rescue it (will this push the read/write console for 
> domains upper on the to-do list?:-)

We should be restoring the VIF state. Unfortunately, this is not
currently part of the suspend record, so needs to be done manually.

>         The 'cpu_time' displayed by 'xc list' of the saved and then restored 
> domain seems not accurate, I am not entirely sure about this I will try to 
> reproduce and report later. Be aware that the restore function starts the 
> domain in the newest domain_id rather than it's orginal id, so the IP address 
> of it would look different to the new domain_id after restored. I have 
> experieced once (I remember when using just 8/16MB memory) that after a 
> domain is restored it keeps generate error message like the followings, is 
> this normal?
>
> ===========================================================
> DOM17: EXT3-fs error (device hd(3,11)) in ext3_reserve_inode_write: IO failure


I haven't seen them before, but we haven't had much external
testing of suspend/resume yet.

Cheers,
Ian

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