Re: [Qemu-devel] bad performance accessing nfs exports on qemu host

[Henning Sprang]

Hi,
I found some answers/help to my questions by further looking:

On Tue, 2005-10-04 at 15:41 +0200, Henning Sprang wrote:
> Hi,
> First of all, this is more a question about qemu usage, not development,
> but the link to the qemu user forum on the qemu website
> ( http://www.dad-answers.com/qemu-forum/index.php )is broken (404), and
> I don't see any other place to get qemu help for users. If there is a
> better place for this question, please tell me so.

The Link on the website is really broken, but I found the user forum on
http://qemu.dad-answers.com/ - it could help users and developers a lot
if that link could be fixed.

I also wonder why there is no Mailing list for users.


> 
> I am trying to use qemu for helping me with the development of an
> automatic installation software for Debian Linux (FAI, that is).
> 
> Therefore I need a qemu guest system (FAI install client) mounting it's
> root file system from an nfs server on the qemu host, and unpacking a
> tar.gz file from that root into a directory from it's "local" virtual
> harddisk.
> 
> While all the other services involved (dhcp, dns, ssh) seem to work with
> no problems, I have serious performance trouble with NFS when I want to
> copy  or unzip the file mentioned. I get a mount, and, when copying the
> file, the whole qemu guest system turns incredibly slow, and it takes
> approximately half an hour to copy a 40M file from the nfsroot to it's
> local disk. In that time, also any command given on the qemu guest's
> shell executes extremly slow. Copying files with ftp is much faster.
> There is not big  CPU load or anything to be seen on neither guest or
> host. So finally everything works, and my automatic install comes to an
> end, but with a very long delay, taking a sum of more than an hour, of
> which most of the seems to be spent on just copying a 40M file.
> 

I found a workaround for that - when I enable NFS over TCP by giving my
install client a line like this with dhcp:

  option root-path
"/usr/lib/fai/nfsroot,rsize=8192,wsize=8192,acregmin=1800,acregmax=1800,acdirmin=1800,acdirmax=1800,tcp";

- most important is the last part "tcp" - then everything goes much much
faster. It seems like qemu doesn't work well for udp packets, maybe the
developers have a better idea and explanation for that?!

Anyway, have a nice day - mine is made by this great thing I found, now
I can use qemu for real nice testing of FAI installation without
spending lots of money for hardware.

Henning