Rsync / ssh high cpu load

Jan Alphenaar jan.alphenaar at
Tue Feb 16 09:31:02 MST 2010

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

	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.



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