Re: [Qemu-devel] [PATCH 0/3] Live migration without shared storage

[lsorense@csclub.uwaterloo.ca (Lennart Sorensen)]

On Mon, Sep 07, 2009 at 06:40:51PM +0200, Pierre Riteau wrote:
> I'm trying blk migration (not incremental) between two machines  
> connected over Gigabit ethernet.
> The transfer is quite slow (about 2 MB/s over the wire).
> While the load on the sending end is low (vmstat says ~2000 blocks in/ 
> sec, and top says ~1% in io wait), on the receiving end I see almost 40% 
> CPU in io wait, kjournald takes 20% of the CPU and vmstat reports ~14000 
> blocks out/sec.
>
> Hosts are running Debian Lenny (2.6.26 32 bits), kvm-87 + your patches.
> The guest is also running Debian Lenny and is idle io wise. I tried with 
> both idle and full cpu utilization, it doesn't change anything.

If you happen to be using ext3, then that might explain it.  ext3 has
long had issues with performance while slowly writing a large file
(this affects mythtv a lot for example).  2.6.30 should improve things a
lot, although ext3 will never be great.  ext4 is better, and hopefully
btrfs will be great (when done).  xfs is also supposed to handle such
tasks very well.

-- 
Len Sorensen