Rsync / ssh high cpu load

[Jan Alphenaar]

Hi,

In an attempt to narrow this down a bit I installed a RedHat machine with
openssh-5.3p1 and rsync-3.0.7 and did the same test as below.

Transferring data, both up and downstream, are not giving me any CPU load.

Although there is a small version difference in the rsync versions, I would
say that this is caused by the cygwin layer.

I will mention this in the cygwin list.

Still, if anybody has any ideas how to solve the issue below, please let me
know.

Warm regards,

Jan

-----Oorspronkelijk bericht-----
Van: Jan Alphenaar [mailto:jan.alphenaar at dotcolour.com] 
Verzonden: dinsdag 16 februari 2010 17:31
Aan: 'rsync at lists.samba.org'
Onderwerp: Rsync / ssh high cpu load

Hi everybody,

I am using Cygwin rsync/ssh to synchronize my files from my home computer to
my server. I raised a question on the Cygwin list as well, but thought this
list would be appropriate too.

The issue is that the CPU on the sending side is fully allocated by
rsync/ssh (both taking 50%) during a file transfer. This is the command I
use:

	rsync -e ssh * <user>@<server>:/data

After some more testing on this I figured out that rsync/ssh is only taking
the full cpu if the bandwidth allocated to the session exceeds the true
bandwidth available on the link.

For example, if the uplink is 128KB/s and I pass in the --bwlimit=24
parameter the cpu is around 0%. Even --bw-limit=126 does not take 100% cpu,
but --bwlimit=132 does. Note this is the first install, the /data directory
on the receiving side is empty.

Would this be because of packet loss on the link and packets have to be
retransmitted ? I will do a quick test tonight with rsync/ssh between two
linux boxes (without cygwin), see what that gives me.

Note that I am using these versions:

Cygwin: 1.7.1-1
ssh: OpenSSH_5.3p1
rsync: 3.0.6

Has anybody seen this before ?

Thanks in advance.

Regards,

Jan